diff --git a/.drone.yml b/.drone.yml
index f5eca687..9e551d85 100644
--- a/.drone.yml
+++ b/.drone.yml
@@ -511,7 +511,7 @@ steps:
   environment:
     CC: clang
     CXX: clang++
-    CMAKE_FLAGS: -DSIMDJSON_SANITIZE=ON -DSIMDJSON_DISABLE_AVX=ON
+    CMAKE_FLAGS: -DSIMDJSON_SANITIZE=ON -DSIMDJSON_IMPLEMENTATION_HASWELL=OFF
   commands:
     - apt-get update -qq
     - apt-get install -y clang make cmake
@@ -534,7 +534,7 @@ steps:
   environment:
     CC: gcc
     CXX: g++
-    CMAKE_FLAGS: -DSIMDJSON_SANITIZE=ON -DSIMDJSON_DISABLE_AVX=ON
+    CMAKE_FLAGS: -DSIMDJSON_SANITIZE=ON -DSIMDJSON_IMPLEMENTATION_HASWELL=OFF
   commands:
     - apt-get update -qq
     - apt-get install -y cmake
diff --git a/.gitignore b/.gitignore
index 634adf3d..162fa78f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -77,7 +77,8 @@ objs
 /get_corpus_benchmark
 /json2json
 /jsoncheck
-/jsoncheck_noavx
+/jsoncheck_westmere
+/jsoncheck_fallback
 /jsonpointer
 /jsonstats
 /integer_tests
diff --git a/CMakeLists.txt b/CMakeLists.txt
index de0d1980..c5c7e92f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -31,7 +31,10 @@ set(PROJECT_VERSION_PATCH 1)
 set(SIMDJSON_LIB_VERSION "0.2.1" CACHE STRING "simdjson library version")
 set(SIMDJSON_LIB_SOVERSION "0" CACHE STRING "simdjson library soversion")
 
-option(SIMDJSON_DISABLE_AVX "Forcefully disable AVX even if hardware supports it" OFF)
+option(SIMDJSON_IMPLEMENTATION_HASWELL "Include the haswell implementation" ON)
+option(SIMDJSON_IMPLEMENTATION_WESTMERE "Include the westmere implementation" ON)
+option(SIMDJSON_IMPLEMENTATION_ARM64 "Include the arm64 implementation" ON)
+option(SIMDJSON_IMPLEMENTATION_FALLBACK "Include the fallback implementation" ON)
 if(NOT MSVC)
   option(SIMDJSON_BUILD_STATIC "Build a static library" OFF) # turning it on disables the production of a dynamic library
 else()
diff --git a/Makefile b/Makefile
index 020f1ce2..810a74cf 100644
--- a/Makefile
+++ b/Makefile
@@ -61,7 +61,7 @@ endif # ifeq ($(MEMSANITIZE),1)
 SRCHEADERS_GENERIC=src/generic/atomparsing.h src/generic/numberparsing.h src/generic/stage1_find_marks.h src/generic/stage2_build_tape.h src/generic/stringparsing.h src/generic/stage2_streaming_build_tape.h src/generic/utf8_fastvalidate_algorithm.h src/generic/utf8_lookup_algorithm.h src/generic/utf8_lookup2_algorithm.h src/generic/utf8_range_algorithm.h src/generic/utf8_zwegner_algorithm.h
 SRCHEADERS_ARM64=      src/arm64/bitmanipulation.h    src/arm64/bitmask.h    src/arm64/intrinsics.h    src/arm64/numberparsing.h    src/arm64/simd.h    src/arm64/stage1_find_marks.h    src/arm64/stage2_build_tape.h    src/arm64/stringparsing.h
 SRCHEADERS_HASWELL=  src/haswell/bitmanipulation.h  src/haswell/bitmask.h  src/haswell/intrinsics.h  src/haswell/numberparsing.h  src/haswell/simd.h  src/haswell/stage1_find_marks.h  src/haswell/stage2_build_tape.h  src/haswell/stringparsing.h
-SRCHEADERS_FALLBACK=  src/fallback/implementation.h src/fallback/stage1_find_marks.h src/fallback/stage2_build_tape.h
+SRCHEADERS_FALLBACK=  src/fallback/bitmanipulation.h src/fallback/implementation.h src/fallback/numberparsing.h src/fallback/stage1_find_marks.h src/fallback/stage2_build_tape.h src/fallback/stringparsing.h
 SRCHEADERS_WESTMERE=src/westmere/bitmanipulation.h src/westmere/bitmask.h src/westmere/intrinsics.h src/westmere/numberparsing.h src/westmere/simd.h src/westmere/stage1_find_marks.h src/westmere/stage2_build_tape.h src/westmere/stringparsing.h
 SRCHEADERS_SRC=src/isadetection.h src/jsoncharutils.h src/simdprune_tables.h src/implementation.cpp src/stage1_find_marks.cpp src/stage2_build_tape.cpp src/document_parser_callbacks.h
 SRCHEADERS=$(SRCHEADERS_SRC) $(SRCHEADERS_GENERIC) $(SRCHEADERS_ARM64) $(SRCHEADERS_HASWELL) $(SRCHEADERS_WESTMERE) $(SRCHEADERS_FALLBACK)
@@ -96,7 +96,7 @@ JSON_INCLUDE:=dependencies/json/single_include/nlohmann/json.hpp
 EXTRAOBJECTS=ujdecode.o
 
 MAINEXECUTABLES=parse minify json2json jsonstats statisticalmodel jsonpointer get_corpus_benchmark
-TESTEXECUTABLES=jsoncheck jsoncheck_noavx integer_tests numberparsingcheck stringparsingcheck pointercheck parse_many_test basictests errortests readme_examples
+TESTEXECUTABLES=jsoncheck jsoncheck_westmere jsoncheck_fallback integer_tests numberparsingcheck stringparsingcheck pointercheck parse_many_test basictests errortests readme_examples
 COMPARISONEXECUTABLES=minifiercompetition parsingcompetition parseandstatcompetition distinctuseridcompetition allparserscheckfile allparsingcompetition
 SUPPLEMENTARYEXECUTABLES=parse_noutf8validation parse_nonumberparsing parse_nostringparsing
 
@@ -134,8 +134,11 @@ run_jsoncheck: jsoncheck
 run_parse_many_test: parse_many_test
 	./parse_many_test
 
-run_jsoncheck_noavx: jsoncheck_noavx
-	./jsoncheck_noavx
+run_jsoncheck_westmere: jsoncheck_westmere
+	./jsoncheck_westmere
+
+run_jsoncheck_fallback: jsoncheck_fallback
+	./jsoncheck_fallback
 
 run_pointercheck: pointercheck
 	./pointercheck
@@ -152,12 +155,12 @@ $(FEATURE_JSON_FILES): benchmark/genfeaturejson.rb
 run_benchfeatures: benchfeatures $(FEATURE_JSON_FILES)
 	./benchfeatures -n 1000
 
-test: run_basictests run_readme_examples run_jsoncheck run_numberparsingcheck run_integer_tests run_stringparsingcheck  run_parse_many_test run_pointercheck run_testjson2json_sh run_issue150_sh run_jsoncheck_noavx
+test: run_basictests run_readme_examples run_jsoncheck run_numberparsingcheck run_integer_tests run_stringparsingcheck  run_parse_many_test run_pointercheck run_testjson2json_sh run_issue150_sh run_jsoncheck_westmere run_jsoncheck_fallback
 	@echo "It looks like the code is good!"
 
-quiettest: run_basictests run_readme_examples run_jsoncheck run_numberparsingcheck run_integer_tests run_stringparsingcheck run_jsoncheck run_parse_many_test run_pointercheck run_testjson2json_sh run_issue150_sh run_jsoncheck_noavx
+quiettest: run_basictests run_readme_examples run_jsoncheck run_numberparsingcheck run_integer_tests run_stringparsingcheck run_jsoncheck run_parse_many_test run_pointercheck run_testjson2json_sh run_issue150_sh run_jsoncheck_westmere run_jsoncheck_fallback
 
-quicktests: run_basictests run_readme_examples run_jsoncheck run_numberparsingcheck run_integer_tests run_stringparsingcheck run_jsoncheck run_parse_many_test run_pointercheck run_jsoncheck_noavx
+quicktests: run_basictests run_readme_examples run_jsoncheck run_numberparsingcheck run_integer_tests run_stringparsingcheck run_jsoncheck run_parse_many_test run_pointercheck run_jsoncheck_westmere run_jsoncheck_fallback
 
 slowtests: run_testjson2json_sh run_issue150_sh
 
@@ -215,8 +218,11 @@ parse_many_test:tests/parse_many_test.cpp $(HEADERS) $(LIBFILES)
 	$(CXX) $(CXXFLAGS) -o parse_many_test tests/parse_many_test.cpp -I. $(LIBFILES) $(LIBFLAGS)
 
 
-jsoncheck_noavx:tests/jsoncheck.cpp $(HEADERS) $(LIBFILES)
-	$(CXX) $(CXXFLAGS) -o jsoncheck_noavx tests/jsoncheck.cpp -I. $(LIBFILES) $(LIBFLAGS) -DSIMDJSON_DISABLE_AVX2_DETECTION
+jsoncheck_westmere:tests/jsoncheck.cpp $(HEADERS) $(LIBFILES)
+	$(CXX) $(CXXFLAGS) -o jsoncheck_westmere tests/jsoncheck.cpp -I. $(LIBFILES) $(LIBFLAGS) -DSIMDJSON_IMPLEMENTATION_HASWELL=0
+
+jsoncheck_fallback:tests/jsoncheck.cpp $(HEADERS) $(LIBFILES)
+	$(CXX) $(CXXFLAGS) -o jsoncheck_fallback tests/jsoncheck.cpp -I. $(LIBFILES) $(LIBFLAGS) -DSIMDJSON_IMPLEMENTATION_HASWELL=0 -DSIMDJSON_IMPLEMENTATION_WESTMERE=0 -DSIMDJSON_IMPLEMENTATION_ARM64=0
 
 basictests:tests/basictests.cpp $(HEADERS) $(LIBFILES)
 	$(CXX) $(CXXFLAGS) -o basictests tests/basictests.cpp -I. $(LIBFILES) $(LIBFLAGS)
diff --git a/fuzz/build_fuzzer_variants.sh b/fuzz/build_fuzzer_variants.sh
index 6fc1afb6..75bc39fb 100755
--- a/fuzz/build_fuzzer_variants.sh
+++ b/fuzz/build_fuzzer_variants.sh
@@ -25,7 +25,7 @@ if [ ! -d build-$variant ] ; then
 	  -DSIMDJSON_BUILD_STATIC=On \
 	  -DENABLE_FUZZING=On \
 	  -DSIMDJSON_FUZZ_LINKMAIN=On \
-	  -DSIMDJSON_DISABLE_AVX=On
+	  -DSIMDJSON_IMPLEMENTATION_HASWELL=0
     
     ninja
     cd ..
@@ -69,7 +69,7 @@ if [ ! -d build-$variant ] ; then
 	  -DENABLE_FUZZING=On \
 	  -DSIMDJSON_FUZZ_LINKMAIN=Off \
 	  -DSIMDJSON_FUZZ_LDFLAGS=$LIB_FUZZING_ENGINE \
-	  -DSIMDJSON_DISABLE_AVX=On
+	  -DSIMDJSON_IMPLEMENTATION_HASWELL=0
     
     ninja
     cd ..
@@ -97,7 +97,7 @@ if which clang++-8 >/dev/null 2>&1 ; then
 	      -DENABLE_FUZZING=On \
 	      -DSIMDJSON_FUZZ_LINKMAIN=Off \
 	      -DSIMDJSON_FUZZ_LDFLAGS=$LIB_FUZZING_ENGINE \
-	      -DSIMDJSON_DISABLE_AVX=On
+	      -DSIMDJSON_IMPLEMENTATION_HASWELL=0
 	
 	ninja
 	cd ..
diff --git a/include/simdjson/portability.h b/include/simdjson/portability.h
index c4dac8be..2f8072b2 100644
--- a/include/simdjson/portability.h
+++ b/include/simdjson/portability.h
@@ -21,6 +21,28 @@
 #define STRINGIFY_IMPLEMENTATION_(a) #a
 #define STRINGIFY(a) STRINGIFY_IMPLEMENTATION_(a)
 
+#ifndef SIMDJSON_IMPLEMENTATION_FALLBACK
+#define SIMDJSON_IMPLEMENTATION_FALLBACK 1
+#endif
+
+#if IS_ARM64
+#ifndef SIMDJSON_IMPLEMENTATION_ARM64
+#define SIMDJSON_IMPLEMENTATION_ARM64 1
+#endif
+#define SIMDJSON_IMPLEMENTATION_HASWELL 0
+#define SIMDJSON_IMPLEMENTATION_WESTMERE 0
+#endif // IS_ARM64
+
+#if IS_X86_64
+#ifndef SIMDJSON_IMPLEMENTATION_HASWELL
+#define SIMDJSON_IMPLEMENTATION_HASWELL 1
+#endif
+#ifndef SIMDJSON_IMPLEMENTATION_WESTMERE
+#define SIMDJSON_IMPLEMENTATION_WESTMERE 1
+#endif
+#define SIMDJSON_IMPLEMENTATION_ARM64 0
+#endif // IS_X86_64
+
 // we are going to use runtime dispatch
 #ifdef IS_X86_64
 #ifdef __clang__
diff --git a/singleheader/simdjson.cpp b/singleheader/simdjson.cpp
index 9ad1fdd4..ba25e97a 100644
--- a/singleheader/simdjson.cpp
+++ b/singleheader/simdjson.cpp
@@ -191,11 +191,9 @@ static inline uint32_t detect_supported_architectures() {
   eax = 0x7;
   ecx = 0x0;
   cpuid(&eax, &ebx, &ecx, &edx);
-#ifndef SIMDJSON_DISABLE_AVX2_DETECTION
   if (ebx & cpuid_avx2_bit) {
     host_isa |= instruction_set::AVX2;
   }
-#endif 
   if (ebx & cpuid_bmi1_bit) {
     host_isa |= instruction_set::BMI1;
   }
diff --git a/src/arm64/bitmanipulation.h b/src/arm64/bitmanipulation.h
index cdc6278c..da00e7db 100644
--- a/src/arm64/bitmanipulation.h
+++ b/src/arm64/bitmanipulation.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_ARM64_BITMANIPULATION_H
 
 #include "simdjson.h"
-
-#ifdef IS_ARM64
-
 #include "arm64/intrinsics.h"
 
 namespace simdjson::arm64 {
@@ -83,6 +80,4 @@ really_inline bool mul_overflow(uint64_t value1, uint64_t value2, uint64_t *resu
 
 } // namespace simdjson::arm64
 
-#endif // IS_ARM64
-
 #endif // SIMDJSON_ARM64_BITMANIPULATION_H
diff --git a/src/arm64/bitmask.h b/src/arm64/bitmask.h
index 81a69c64..11f39a4d 100644
--- a/src/arm64/bitmask.h
+++ b/src/arm64/bitmask.h
@@ -3,8 +3,6 @@
 
 #include "simdjson.h"
 
-#ifdef IS_ARM64
-
 #include "arm64/intrinsics.h"
 
 namespace simdjson::arm64 {
@@ -40,5 +38,4 @@ really_inline uint64_t prefix_xor(uint64_t bitmask) {
 } // namespace simdjson::arm64
 UNTARGET_REGION
 
-#endif // IS_ARM64
 #endif
diff --git a/src/arm64/implementation.h b/src/arm64/implementation.h
index 56650509..4766cb4e 100644
--- a/src/arm64/implementation.h
+++ b/src/arm64/implementation.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_ARM64_IMPLEMENTATION_H
 
 #include "simdjson.h"
-
-#ifdef IS_ARM64
-
 #include "isadetection.h"
 
 namespace simdjson::arm64 {
@@ -20,6 +17,4 @@ public:
 
 } // namespace simdjson::arm64
 
-#endif // IS_ARM64
-
 #endif // SIMDJSON_ARM64_IMPLEMENTATION_H
diff --git a/src/arm64/intrinsics.h b/src/arm64/intrinsics.h
index 71813c5a..ceebaf24 100644
--- a/src/arm64/intrinsics.h
+++ b/src/arm64/intrinsics.h
@@ -3,11 +3,8 @@
 
 #include "simdjson.h"
 
-#ifdef IS_ARM64
-
 // This should be the correct header whether
 // you use visual studio or other compilers.
 #include <arm_neon.h>
 
-#endif //   IS_ARM64
 #endif //  SIMDJSON_ARM64_INTRINSICS_H
diff --git a/src/arm64/numberparsing.h b/src/arm64/numberparsing.h
index 4c8c54a4..03523a42 100644
--- a/src/arm64/numberparsing.h
+++ b/src/arm64/numberparsing.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_ARM64_NUMBERPARSING_H
 
 #include "simdjson.h"
-
-#ifdef IS_ARM64
-
 #include "jsoncharutils.h"
 #include "arm64/intrinsics.h"
 #include "arm64/bitmanipulation.h"
@@ -35,9 +32,6 @@ static inline uint32_t parse_eight_digits_unrolled(const char *chars) {
 
 #include "generic/numberparsing.h"
 
+} // namespace simdjson::arm64
 
-}// namespace simdjson::arm64
-
-
-#endif // IS_ARM64
-#endif //  SIMDJSON_ARM64_NUMBERPARSING_H
+#endif // SIMDJSON_ARM64_NUMBERPARSING_H
diff --git a/src/arm64/simd.h b/src/arm64/simd.h
index 0c13dfb4..bb21b273 100644
--- a/src/arm64/simd.h
+++ b/src/arm64/simd.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_ARM64_SIMD_H
 
 #include "simdjson.h"
-
-#ifdef IS_ARM64
-
 #include "arm64/intrinsics.h"
 
 namespace simdjson::arm64::simd {
@@ -347,5 +344,4 @@ namespace simdjson::arm64::simd {
 
 } // namespace simdjson::arm64::simd
 
-#endif // IS_ARM64
 #endif // SIMDJSON_ARM64_SIMD_H
diff --git a/src/arm64/stage1_find_marks.h b/src/arm64/stage1_find_marks.h
index 62665b78..7a15921b 100644
--- a/src/arm64/stage1_find_marks.h
+++ b/src/arm64/stage1_find_marks.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_ARM64_STAGE1_FIND_MARKS_H
 
 #include "simdjson.h"
-
-#ifdef IS_ARM64
-
 #include "arm64/bitmask.h"
 #include "arm64/simd.h"
 #include "arm64/bitmanipulation.h"
@@ -56,6 +53,4 @@ WARN_UNUSED error_code implementation::stage1(const uint8_t *buf, size_t len, do
 
 } // namespace simdjson::arm64
 
-#endif // IS_ARM64
-
 #endif // SIMDJSON_ARM64_STAGE1_FIND_MARKS_H
diff --git a/src/arm64/stage2_build_tape.h b/src/arm64/stage2_build_tape.h
index 7179e2c4..2b711157 100644
--- a/src/arm64/stage2_build_tape.h
+++ b/src/arm64/stage2_build_tape.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_ARM64_STAGE2_BUILD_TAPE_H
 
 #include "simdjson.h"
-
-#ifdef IS_ARM64
-
 #include "arm64/implementation.h"
 #include "arm64/stringparsing.h"
 #include "arm64/numberparsing.h"
@@ -17,6 +14,4 @@ namespace simdjson::arm64 {
 
 } // namespace simdjson::arm64
 
-#endif // IS_ARM64
-
 #endif // SIMDJSON_ARM64_STAGE2_BUILD_TAPE_H
diff --git a/src/arm64/stringparsing.h b/src/arm64/stringparsing.h
index 3cd78dee..7dd9db68 100644
--- a/src/arm64/stringparsing.h
+++ b/src/arm64/stringparsing.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_ARM64_STRINGPARSING_H
 
 #include "simdjson.h"
-
-#ifdef IS_ARM64
-
 #include "jsoncharutils.h"
 #include "arm64/simd.h"
 #include "arm64/intrinsics.h"
@@ -52,6 +49,4 @@ really_inline backslash_and_quote backslash_and_quote::copy_and_find(const uint8
 }
 // namespace simdjson::amd64
 
-#endif // IS_ARM64
-
 #endif // SIMDJSON_ARM64_STRINGPARSING_H
diff --git a/src/haswell/bitmanipulation.h b/src/haswell/bitmanipulation.h
index 31397155..6ef91a97 100644
--- a/src/haswell/bitmanipulation.h
+++ b/src/haswell/bitmanipulation.h
@@ -3,8 +3,6 @@
 
 #include "simdjson.h"
 
-#ifdef IS_X86_64
-
 #include "haswell/intrinsics.h"
 
 TARGET_HASWELL
@@ -76,6 +74,4 @@ really_inline bool mul_overflow(uint64_t value1, uint64_t value2,
 }// namespace simdjson::haswell
 UNTARGET_REGION
 
-#endif // IS_X86_64
-
 #endif // SIMDJSON_HASWELL_BITMANIPULATION_H
diff --git a/src/haswell/bitmask.h b/src/haswell/bitmask.h
index 3ef707a8..f97272e6 100644
--- a/src/haswell/bitmask.h
+++ b/src/haswell/bitmask.h
@@ -3,8 +3,6 @@
 
 #include "simdjson.h"
 
-#ifdef IS_X86_64
-
 #include "haswell/intrinsics.h"
 
 TARGET_HASWELL
@@ -26,6 +24,4 @@ really_inline uint64_t prefix_xor(const uint64_t bitmask) {
 } // namespace simdjson::haswell
 UNTARGET_REGION
 
-#endif // IS_X86_64
-
 #endif // SIMDJSON_HASWELL_BITMASK_H
diff --git a/src/haswell/implementation.h b/src/haswell/implementation.h
index 5dec34d5..d9f50514 100644
--- a/src/haswell/implementation.h
+++ b/src/haswell/implementation.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_HASWELL_IMPLEMENTATION_H
 
 #include "simdjson.h"
-
-#ifdef IS_X86_64
-
 #include "isadetection.h"
 
 namespace simdjson::haswell {
@@ -24,6 +21,4 @@ public:
 
 } // namespace simdjson::haswell
 
-#endif // IS_X86_64
-
 #endif // SIMDJSON_HASWELL_IMPLEMENTATION_H
\ No newline at end of file
diff --git a/src/haswell/intrinsics.h b/src/haswell/intrinsics.h
index b426de90..bc978822 100644
--- a/src/haswell/intrinsics.h
+++ b/src/haswell/intrinsics.h
@@ -3,14 +3,10 @@
 
 #include "simdjson.h"
 
-#ifdef IS_X86_64
-
 #ifdef _MSC_VER
 #include <intrin.h> // visual studio
 #else
 #include <x86intrin.h> // elsewhere
 #endif // _MSC_VER
 
-#endif // IS_X86_64
-
 #endif // SIMDJSON_HASWELL_INTRINSICS_H
diff --git a/src/haswell/numberparsing.h b/src/haswell/numberparsing.h
index 7307ee41..41ad4246 100644
--- a/src/haswell/numberparsing.h
+++ b/src/haswell/numberparsing.h
@@ -3,8 +3,6 @@
 
 #include "simdjson.h"
 
-#ifdef IS_X86_64
-
 #include "jsoncharutils.h"
 #include "haswell/intrinsics.h"
 #include "haswell/bitmanipulation.h"
@@ -45,6 +43,4 @@ static inline uint32_t parse_eight_digits_unrolled(const char *chars) {
 } // namespace simdjson::haswell
 UNTARGET_REGION
 
-#endif // IS_X86_64
-
 #endif // SIMDJSON_HASWELL_NUMBERPARSING_H
diff --git a/src/haswell/simd.h b/src/haswell/simd.h
index 396376ec..4850dabb 100644
--- a/src/haswell/simd.h
+++ b/src/haswell/simd.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_HASWELL_SIMD_H
 
 #include "simdjson.h"
-
-#ifdef IS_X86_64
-
 #include "haswell/intrinsics.h"
 
 TARGET_HASWELL
@@ -311,6 +308,4 @@ namespace simdjson::haswell::simd {
 } // namespace simdjson::haswell::simd
 UNTARGET_REGION
 
-#endif // IS_X86_64
-
 #endif // SIMDJSON_HASWELL_SIMD_H
diff --git a/src/haswell/stage1_find_marks.h b/src/haswell/stage1_find_marks.h
index 97dab6a8..4c19e930 100644
--- a/src/haswell/stage1_find_marks.h
+++ b/src/haswell/stage1_find_marks.h
@@ -3,8 +3,6 @@
 
 #include "simdjson.h"
 
-#ifdef IS_X86_64
-
 #include "haswell/bitmask.h"
 #include "haswell/simd.h"
 #include "haswell/bitmanipulation.h"
@@ -55,6 +53,4 @@ WARN_UNUSED error_code implementation::stage1(const uint8_t *buf, size_t len, do
 } // namespace simdjson::haswell
 UNTARGET_REGION
 
-#endif // IS_X86_64
-
 #endif // SIMDJSON_HASWELL_STAGE1_FIND_MARKS_H
diff --git a/src/haswell/stage2_build_tape.h b/src/haswell/stage2_build_tape.h
index 8f22d54e..34560779 100644
--- a/src/haswell/stage2_build_tape.h
+++ b/src/haswell/stage2_build_tape.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_HASWELL_STAGE2_BUILD_TAPE_H
 
 #include "simdjson.h"
-
-#ifdef IS_X86_64
-
 #include "haswell/implementation.h"
 #include "haswell/stringparsing.h"
 #include "haswell/numberparsing.h"
@@ -19,6 +16,4 @@ namespace simdjson::haswell {
 } // namespace simdjson
 UNTARGET_REGION
 
-#endif // IS_X86_64
-
 #endif // SIMDJSON_HASWELL_STAGE2_BUILD_TAPE_H
diff --git a/src/haswell/stringparsing.h b/src/haswell/stringparsing.h
index 78cfae62..6e6a633c 100644
--- a/src/haswell/stringparsing.h
+++ b/src/haswell/stringparsing.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_HASWELL_STRINGPARSING_H
 
 #include "simdjson.h"
-
-#ifdef IS_X86_64
-
 #include "jsoncharutils.h"
 #include "haswell/simd.h"
 #include "haswell/intrinsics.h"
@@ -48,6 +45,4 @@ really_inline backslash_and_quote backslash_and_quote::copy_and_find(const uint8
 } // namespace simdjson::haswell
 UNTARGET_REGION
 
-#endif // IS_X86_64
-
 #endif // SIMDJSON_HASWELL_STRINGPARSING_H
diff --git a/src/implementation.cpp b/src/implementation.cpp
index b1c446bc..5d40df29 100644
--- a/src/implementation.cpp
+++ b/src/implementation.cpp
@@ -1,39 +1,46 @@
 #include "simdjson.h"
+#include "isadetection.h"
 #include <initializer_list>
 
 // Static array of known implementations. We're hoping these get baked into the executable
 // without requiring a static initializer.
 
-#ifdef IS_X86_64
-
+#if SIMDJSON_IMPLEMENTATION_HASWELL
 #include "haswell/implementation.h"
+namespace simdjson::internal { const haswell::implementation haswell_singleton{}; }
+#endif // SIMDJSON_IMPLEMENTATION_HASWELL
+
+#if SIMDJSON_IMPLEMENTATION_WESTMERE
 #include "westmere/implementation.h"
-#include "fallback/implementation.h"
-
-namespace simdjson::internal {
-const fallback::implementation fallback_singleton{};
-const haswell::implementation haswell_singleton{};
-const westmere::implementation westmere_singleton{};
-constexpr const std::initializer_list<const implementation *> available_implementation_pointers { &haswell_singleton, &westmere_singleton, &fallback_singleton };
-}
-
-#endif
-
-#ifdef IS_ARM64
+namespace simdjson::internal { const westmere::implementation westmere_singleton{}; }
+#endif // SIMDJSON_IMPLEMENTATION_WESTMERE
 
+#if SIMDJSON_IMPLEMENTATION_ARM64
 #include "arm64/implementation.h"
+namespace simdjson::internal { const arm64::implementation arm64_singleton{}; }
+#endif // SIMDJSON_IMPLEMENTATION_ARM64
+
+#if SIMDJSON_IMPLEMENTATION_FALLBACK
 #include "fallback/implementation.h"
+namespace simdjson::internal { const fallback::implementation fallback_singleton{}; }
+#endif // SIMDJSON_IMPLEMENTATION_FALLBACK
 
 namespace simdjson::internal {
-const fallback::implementation fallback_singleton{};
-const arm64::implementation arm64_singleton{};
-constexpr const std::initializer_list<const implementation *> available_implementation_pointers { &arm64_singleton, &fallback_singleton };
-}
 
+constexpr const std::initializer_list<const implementation *> available_implementation_pointers {
+#if SIMDJSON_IMPLEMENTATION_HASWELL
+  &haswell_singleton,
 #endif
-
-
-namespace simdjson::internal {
+#if SIMDJSON_IMPLEMENTATION_WESTMERE
+  &westmere_singleton,
+#endif
+#if SIMDJSON_IMPLEMENTATION_ARM64
+  &arm64_singleton,
+#endif
+#if SIMDJSON_IMPLEMENTATION_FALLBACK
+  &fallback_singleton,
+#endif
+}; // available_implementation_pointers
 
 // So we can return UNSUPPORTED_ARCHITECTURE from the parser when there is no support
 class unsupported_implementation final : public implementation {
@@ -79,4 +86,4 @@ const implementation *detect_best_supported_implementation_on_first_use::set_bes
   return active_implementation = available_implementations.detect_best_supported();
 }
 
-} // namespace simdjson
+} // namespace simdjson::internal
diff --git a/src/isadetection.h b/src/isadetection.h
index c881c85f..b7047598 100644
--- a/src/isadetection.h
+++ b/src/isadetection.h
@@ -120,11 +120,9 @@ static inline uint32_t detect_supported_architectures() {
   eax = 0x7;
   ecx = 0x0;
   cpuid(&eax, &ebx, &ecx, &edx);
-#ifndef SIMDJSON_DISABLE_AVX2_DETECTION
   if (ebx & cpuid_avx2_bit) {
     host_isa |= instruction_set::AVX2;
   }
-#endif 
   if (ebx & cpuid_bmi1_bit) {
     host_isa |= instruction_set::BMI1;
   }
diff --git a/src/stage1_find_marks.cpp b/src/stage1_find_marks.cpp
index 5ea28617..338b954a 100644
--- a/src/stage1_find_marks.cpp
+++ b/src/stage1_find_marks.cpp
@@ -1,4 +1,12 @@
+#if SIMDJSON_IMPLEMENTATION_ARM64
 #include "arm64/stage1_find_marks.h"
+#endif
+#if SIMDJSON_IMPLEMENTATION_FALLBACK
 #include "fallback/stage1_find_marks.h"
+#endif
+#if SIMDJSON_IMPLEMENTATION_HASWELL
 #include "haswell/stage1_find_marks.h"
+#endif
+#if SIMDJSON_IMPLEMENTATION_WESTMERE
 #include "westmere/stage1_find_marks.h"
+#endif
diff --git a/src/stage2_build_tape.cpp b/src/stage2_build_tape.cpp
index c0d1919d..2a525ceb 100644
--- a/src/stage2_build_tape.cpp
+++ b/src/stage2_build_tape.cpp
@@ -12,7 +12,15 @@ void found_string(const uint8_t *buf, const uint8_t *parsed_begin,
 void found_bad_string(const uint8_t *buf);
 #endif
 
+#if SIMDJSON_IMPLEMENTATION_ARM64
 #include "arm64/stage2_build_tape.h"
+#endif
+#if SIMDJSON_IMPLEMENTATION_FALLBACK
 #include "fallback/stage2_build_tape.h"
+#endif
+#if SIMDJSON_IMPLEMENTATION_HASWELL
 #include "haswell/stage2_build_tape.h"
+#endif
+#if SIMDJSON_IMPLEMENTATION_WESTMERE
 #include "westmere/stage2_build_tape.h"
+#endif
diff --git a/src/westmere/bitmanipulation.h b/src/westmere/bitmanipulation.h
index 81b68180..e6c7e45b 100644
--- a/src/westmere/bitmanipulation.h
+++ b/src/westmere/bitmanipulation.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_WESTMERE_BITMANIPULATION_H
 
 #include "simdjson.h"
-
-#ifdef IS_X86_64
-
 #include "westmere/intrinsics.h"
 
 TARGET_WESTMERE
@@ -84,9 +81,7 @@ really_inline bool mul_overflow(uint64_t value1, uint64_t value2,
 #endif
 }
 
-}// namespace simdjson::westmere
+} // namespace simdjson::westmere
 UNTARGET_REGION
 
-#endif // IS_X86_64
-
 #endif // SIMDJSON_WESTMERE_BITMANIPULATION_H
diff --git a/src/westmere/bitmask.h b/src/westmere/bitmask.h
index 95ef3802..58eacca3 100644
--- a/src/westmere/bitmask.h
+++ b/src/westmere/bitmask.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_WESTMERE_BITMASK_H
 
 #include "simdjson.h"
-
-#ifdef IS_X86_64
-
 #include "westmere/intrinsics.h"
 
 TARGET_WESTMERE
@@ -26,6 +23,4 @@ really_inline uint64_t prefix_xor(const uint64_t bitmask) {
 } // namespace simdjson::westmere
 UNTARGET_REGION
 
-#endif // IS_X86_64
-
 #endif // SIMDJSON_WESTMERE_BITMASK_H
diff --git a/src/westmere/implementation.h b/src/westmere/implementation.h
index 029743d6..4675867e 100644
--- a/src/westmere/implementation.h
+++ b/src/westmere/implementation.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_WESTMERE_IMPLEMENTATION_H
 
 #include "simdjson.h"
-
-#ifdef IS_X86_64
-
 #include "simdjson/implementation.h"
 #include "isadetection.h"
 
@@ -21,6 +18,4 @@ public:
 
 } // namespace simdjson::westmere
 
-#endif // IS_X86_64
-
 #endif // SIMDJSON_WESTMERE_IMPLEMENTATION_H
\ No newline at end of file
diff --git a/src/westmere/intrinsics.h b/src/westmere/intrinsics.h
index 129bbd1b..127dce96 100644
--- a/src/westmere/intrinsics.h
+++ b/src/westmere/intrinsics.h
@@ -1,12 +1,10 @@
 #ifndef SIMDJSON_WESTMERE_INTRINSICS_H
 #define SIMDJSON_WESTMERE_INTRINSICS_H
 
-#ifdef IS_X86_64
 #ifdef _MSC_VER
 #include <intrin.h> // visual studio
 #else
 #include <x86intrin.h> // elsewhere
 #endif // _MSC_VER
-#endif // IS_X86_64
 
 #endif // SIMDJSON_WESTMERE_INTRINSICS_H
diff --git a/src/westmere/numberparsing.h b/src/westmere/numberparsing.h
index f12d38b5..cf039498 100644
--- a/src/westmere/numberparsing.h
+++ b/src/westmere/numberparsing.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_WESTMERE_NUMBERPARSING_H
 
 #include "simdjson.h"
-
-#ifdef IS_X86_64
-
 #include "jsoncharutils.h"
 #include "westmere/intrinsics.h"
 #include "westmere/bitmanipulation.h"
@@ -47,7 +44,4 @@ static inline uint32_t parse_eight_digits_unrolled(const char *chars) {
 } // namespace simdjson::westmere
 UNTARGET_REGION
 
-
-
-#endif // IS_X86_64
 #endif //  SIMDJSON_WESTMERE_NUMBERPARSING_H
diff --git a/src/westmere/simd.h b/src/westmere/simd.h
index b97f9bd2..c399a7a4 100644
--- a/src/westmere/simd.h
+++ b/src/westmere/simd.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_WESTMERE_SIMD_H
 
 #include "simdjson.h"
-
-#ifdef IS_X86_64
-
 #include "westmere/intrinsics.h"
 
 TARGET_WESTMERE
@@ -311,5 +308,4 @@ namespace simdjson::westmere::simd {
 } // namespace simdjson::westmere::simd
 UNTARGET_REGION
 
-#endif // IS_X86_64
 #endif // SIMDJSON_WESTMERE_SIMD_INPUT_H
diff --git a/src/westmere/stage1_find_marks.h b/src/westmere/stage1_find_marks.h
index b3e2ad1e..c229a232 100644
--- a/src/westmere/stage1_find_marks.h
+++ b/src/westmere/stage1_find_marks.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_WESTMERE_STAGE1_FIND_MARKS_H
 
 #include "simdjson.h"
-
-#ifdef IS_X86_64
-
 #include "westmere/bitmask.h"
 #include "westmere/simd.h"
 #include "westmere/bitmanipulation.h"
@@ -57,5 +54,4 @@ WARN_UNUSED error_code implementation::stage1(const uint8_t *buf, size_t len, do
 } // namespace simdjson::westmere
 UNTARGET_REGION
 
-#endif // IS_X86_64
 #endif // SIMDJSON_WESTMERE_STAGE1_FIND_MARKS_H
diff --git a/src/westmere/stage2_build_tape.h b/src/westmere/stage2_build_tape.h
index 7d41c4b4..d8c86347 100644
--- a/src/westmere/stage2_build_tape.h
+++ b/src/westmere/stage2_build_tape.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_WESTMERE_STAGE2_BUILD_TAPE_H
 
 #include "simdjson.h"
-
-#ifdef IS_X86_64
-
 #include "westmere/implementation.h"
 #include "westmere/stringparsing.h"
 #include "westmere/numberparsing.h"
@@ -18,7 +15,4 @@ namespace simdjson::westmere {
 
 } // namespace simdjson::westmere
 UNTARGET_REGION
-
-#endif // IS_X86_64
-
 #endif // SIMDJSON_WESTMERE_STAGE2_BUILD_TAPE_H
diff --git a/src/westmere/stringparsing.h b/src/westmere/stringparsing.h
index 44d382f3..1c3a52a3 100644
--- a/src/westmere/stringparsing.h
+++ b/src/westmere/stringparsing.h
@@ -2,9 +2,6 @@
 #define SIMDJSON_WESTMERE_STRINGPARSING_H
 
 #include "simdjson.h"
-
-#ifdef IS_X86_64
-
 #include "jsoncharutils.h"
 #include "westmere/simd.h"
 #include "westmere/intrinsics.h"
@@ -50,6 +47,4 @@ really_inline backslash_and_quote backslash_and_quote::copy_and_find(const uint8
 } // namespace simdjson::westmere
 UNTARGET_REGION
 
-#endif // IS_X86_64
-
 #endif // SIMDJSON_WESTMERE_STRINGPARSING_H
diff --git a/tests/basictests.cpp b/tests/basictests.cpp
index 6d5599f6..f0083c52 100644
--- a/tests/basictests.cpp
+++ b/tests/basictests.cpp
@@ -10,7 +10,9 @@
 #include <string_view>
 #include <sstream>
 #include <utility>
+#ifndef _MSC_VER
 #include <unistd.h>
+#endif
 
 #include "simdjson.h"
 
@@ -1459,7 +1461,8 @@ bool lots_of_brackets() {
 
 int main(int argc, char *argv[]) {
   std::cout << std::unitbuf;
-  char c;
+#ifndef _MSC_VER
+  int c;
   while ((c = getopt(argc, argv, "a:")) != -1) {
     switch (c) {
     case 'a': {
@@ -1476,6 +1479,9 @@ int main(int argc, char *argv[]) {
       return EXIT_FAILURE;
     }
   }
+#else
+  int optind = 1;
+#endif
 
   // this is put here deliberately to check that the documentation is correct (README),
   // should this fail to compile, you should update the documentation:
diff --git a/tests/jsoncheck.cpp b/tests/jsoncheck.cpp
index b8a80b28..32f57b10 100644
--- a/tests/jsoncheck.cpp
+++ b/tests/jsoncheck.cpp
@@ -112,7 +112,28 @@ bool validate(const char *dirname) {
 }
 
 int main(int argc, char *argv[]) {
-  if (argc != 2) {
+#ifndef _MSC_VER
+  int c;
+  while ((c = getopt(argc, argv, "a:")) != -1) {
+    switch (c) {
+    case 'a': {
+      const simdjson::implementation *impl = simdjson::available_implementations[optarg];
+      if (!impl) {
+        fprintf(stderr, "Unsupported architecture value -a %s\n", optarg);
+        return EXIT_FAILURE;
+      }
+      simdjson::active_implementation = impl;
+      break;
+    }
+    default:
+      fprintf(stderr, "Unexpected argument %c\n", c);
+      return EXIT_FAILURE;
+    }
+  }
+#else
+  int optind = 1;
+#endif
+  if ((argc - optind) != 1) {
     std::cerr << "Usage: " << argv[0] << " <directorywithjsonfiles>"
               << std::endl;
 #ifndef SIMDJSON_TEST_DATA_DIR
@@ -126,5 +147,5 @@ int main(int argc, char *argv[]) {
     return validate(SIMDJSON_TEST_DATA_DIR) ? EXIT_SUCCESS : EXIT_FAILURE;
 #endif
   }
-  return validate(argv[1]) ? EXIT_SUCCESS : EXIT_FAILURE;
+  return validate(argv[optind]) ? EXIT_SUCCESS : EXIT_FAILURE;
 }
diff --git a/tools/cmake/FindOptions.cmake b/tools/cmake/FindOptions.cmake
index 81030a9a..2c665a38 100644
--- a/tools/cmake/FindOptions.cmake
+++ b/tools/cmake/FindOptions.cmake
@@ -18,23 +18,6 @@ else ()
     set (X64 FALSE)
 endif ()
 
-if(X64)
-  message(STATUS "Detected x64 processor: ${CMAKE_SYSTEM_PROCESSOR}")
-  if(SIMDJSON_DISABLE_AVX) 
-    message(STATUS "Disabling AVX. No runtime dispatch.")
-    if(NOT MSVC)
-     set (OPT_FLAGS "${OPT_FLAGS} -mno-avx -mno-bmi -mpclmul -msse4.2") #westmere
-    else()
-     set (OPT_FLAGS "${OPT_FLAGS}")
-    endif()
-  else() 
-    if(NOT MSVC)
-      message(STATUS "Assuming Westmere or better")
-      set (OPT_FLAGS "${OPT_FLAGS} -mpclmul -msse4.2")
-    endif()
-  endif()
-endif()
-
 if(SIMDJSON_EXCEPTIONS)
   set(OPT_FLAGS "${OPT_FLAGS} -DSIMDJSON_EXCEPTIONS=1")
 else()