diff --git a/changelog/4980.feature.rst b/changelog/4980.feature.rst
new file mode 100644
index 000000000..40f1de9c1
--- /dev/null
+++ b/changelog/4980.feature.rst
@@ -0,0 +1 @@
+Namespace packages are handled better with ``monkeypatch.syspath_prepend`` and ``testdir.syspathinsert`` (via ``pkg_resources.fixup_namespace_packages``).
diff --git a/src/_pytest/monkeypatch.py b/src/_pytest/monkeypatch.py
index 46d9718da..f6c134664 100644
--- a/src/_pytest/monkeypatch.py
+++ b/src/_pytest/monkeypatch.py
@@ -262,10 +262,15 @@ class MonkeyPatch(object):
 
     def syspath_prepend(self, path):
         """ Prepend ``path`` to ``sys.path`` list of import locations. """
+        from pkg_resources import fixup_namespace_packages
+
         if self._savesyspath is None:
             self._savesyspath = sys.path[:]
         sys.path.insert(0, str(path))
 
+        # https://github.com/pypa/setuptools/blob/d8b901bc/docs/pkg_resources.txt#L162-L171
+        fixup_namespace_packages(str(path))
+
     def chdir(self, path):
         """ Change the current working directory to the specified path.
         Path can be a string or a py.path.local object.
diff --git a/src/_pytest/pytester.py b/src/_pytest/pytester.py
index ffcd2982a..f8a79ebc9 100644
--- a/src/_pytest/pytester.py
+++ b/src/_pytest/pytester.py
@@ -593,11 +593,16 @@ class Testdir(object):
 
         This is undone automatically when this object dies at the end of each
         test.
-
         """
+        from pkg_resources import fixup_namespace_packages
+
         if path is None:
             path = self.tmpdir
-        sys.path.insert(0, str(path))
+
+        dirname = str(path)
+        sys.path.insert(0, dirname)
+        fixup_namespace_packages(dirname)
+
         # a call to syspathinsert() usually means that the caller wants to
         # import some dynamically created files, thus with python3 we
         # invalidate its import caches
@@ -606,12 +611,10 @@ class Testdir(object):
     def _possibly_invalidate_import_caches(self):
         # invalidate caches if we can (py33 and above)
         try:
-            import importlib
+            from importlib import invalidate_caches
         except ImportError:
-            pass
-        else:
-            if hasattr(importlib, "invalidate_caches"):
-                importlib.invalidate_caches()
+            return
+        invalidate_caches()
 
     def mkdir(self, name):
         """Create a new (sub)directory."""
diff --git a/testing/python/collect.py b/testing/python/collect.py
index bc7462674..df6070b8d 100644
--- a/testing/python/collect.py
+++ b/testing/python/collect.py
@@ -34,8 +34,6 @@ class TestModule(object):
         )
 
     def test_import_prepend_append(self, testdir, monkeypatch):
-        syspath = list(sys.path)
-        monkeypatch.setattr(sys, "path", syspath)
         root1 = testdir.mkdir("root1")
         root2 = testdir.mkdir("root2")
         root1.ensure("x456.py")
diff --git a/testing/test_assertrewrite.py b/testing/test_assertrewrite.py
index bdfbf823c..a92ffcf75 100644
--- a/testing/test_assertrewrite.py
+++ b/testing/test_assertrewrite.py
@@ -1335,7 +1335,7 @@ class TestEarlyRewriteBailout(object):
         # Setup conditions for py's fspath trying to import pathlib on py34
         # always (previously triggered via xdist only).
         # Ref: https://github.com/pytest-dev/py/pull/207
-        monkeypatch.setattr(sys, "path", [""] + sys.path)
+        monkeypatch.syspath_prepend("")
         monkeypatch.delitem(sys.modules, "pathlib", raising=False)
 
         testdir.makepyfile(
diff --git a/testing/test_monkeypatch.py b/testing/test_monkeypatch.py
index 0a953d3f1..d43fb6bab 100644
--- a/testing/test_monkeypatch.py
+++ b/testing/test_monkeypatch.py
@@ -437,3 +437,28 @@ def test_context():
         m.setattr(functools, "partial", 3)
         assert not inspect.isclass(functools.partial)
     assert inspect.isclass(functools.partial)
+
+
+def test_syspath_prepend_with_namespace_packages(testdir, monkeypatch):
+    for dirname in "hello", "world":
+        d = testdir.mkdir(dirname)
+        ns = d.mkdir("ns_pkg")
+        ns.join("__init__.py").write(
+            "__import__('pkg_resources').declare_namespace(__name__)"
+        )
+        lib = ns.mkdir(dirname)
+        lib.join("__init__.py").write("def check(): return %r" % dirname)
+
+    monkeypatch.syspath_prepend("hello")
+    import ns_pkg.hello
+
+    assert ns_pkg.hello.check() == "hello"
+
+    with pytest.raises(ImportError):
+        import ns_pkg.world
+
+    # Prepending should call fixup_namespace_packages.
+    monkeypatch.syspath_prepend("world")
+    import ns_pkg.world
+
+    assert ns_pkg.world.check() == "world"
diff --git a/testing/test_pluginmanager.py b/testing/test_pluginmanager.py
index 6b44f3e0c..10b54c112 100644
--- a/testing/test_pluginmanager.py
+++ b/testing/test_pluginmanager.py
@@ -4,7 +4,6 @@ from __future__ import division
 from __future__ import print_function
 
 import os
-import re
 import sys
 import types
 
@@ -165,10 +164,10 @@ def test_importplugin_error_message(testdir, pytestpm):
     with pytest.raises(ImportError) as excinfo:
         pytestpm.import_plugin("qwe")
 
-    expected_message = '.*Error importing plugin "qwe": Not possible to import: .'
-    expected_traceback = ".*in test_traceback"
-    assert re.match(expected_message, str(excinfo.value))
-    assert re.match(expected_traceback, str(excinfo.traceback[-1]))
+    assert str(excinfo.value).endswith(
+        'Error importing plugin "qwe": Not possible to import: ☺'
+    )
+    assert "in test_traceback" in str(excinfo.traceback[-1])
 
 
 class TestPytestPluginManager(object):