diff --git a/contributors.txt b/contributors.txt
index f4f4010c0..e7395e4a5 100644
--- a/contributors.txt
+++ b/contributors.txt
@@ -217,4 +217,5 @@ YYYY/MM/DD, github id, Full name, email
 2019/02/06, ralucado, Cristina Raluca Vijulie, ralucris.v[at]gmail[dot]com
 2019/03/13, base698, Justin Thomas, justin.thomas1@gmail.com
 2019/03/18, carlodri, Carlo Dri, carlo.dri@gmail.com
-2019/05/02, askingalot, Andy Collins, askingalot@gmail.com
\ No newline at end of file
+2019/05/02, askingalot, Andy Collins, askingalot@gmail.com
+2019/07/11, olowo726, Olof Wolgast, olof@baah.se
diff --git a/runtime/Cpp/runtime/src/support/StringUtils.h b/runtime/Cpp/runtime/src/support/StringUtils.h
index d0a0472a0..49715287e 100644
--- a/runtime/Cpp/runtime/src/support/StringUtils.h
+++ b/runtime/Cpp/runtime/src/support/StringUtils.h
@@ -22,7 +22,7 @@ namespace antlrcpp {
   inline std::string utf32_to_utf8(T const& data)
   {
     // Don't make the converter static or we have to serialize access to it.
-    UTF32Converter converter;
+    thread_local UTF32Converter converter;
 
     #if defined(_MSC_VER) && _MSC_VER >= 1900 && _MSC_VER < 2000
       auto p = reinterpret_cast<const int32_t *>(data.data());
@@ -34,7 +34,7 @@ namespace antlrcpp {
 
   inline UTF32String utf8_to_utf32(const char* first, const char* last)
   {
-    UTF32Converter converter;
+    thread_local UTF32Converter converter;
 
     #if defined(_MSC_VER) && _MSC_VER >= 1900 && _MSC_VER < 2000
       auto r = converter.from_bytes(first, last);