diff -r c48583859e04 -r 65cd7e705ff6 contrib/check-py3-compat.py
--- a/contrib/check-py3-compat.py	Fri Aug 12 11:06:14 2016 +0900
+++ b/contrib/check-py3-compat.py	Sat Aug 13 17:21:58 2016 +0900
@@ -14,6 +14,16 @@
 import sys
 import traceback
 
+# Modules that have both Python and C implementations.
+_dualmodules = (
+    'base85.py',
+    'bdiff.py',
+    'diffhelpers.py',
+    'mpatch.py',
+    'osutil.py',
+    'parsers.py',
+)
+
 def check_compat_py2(f):
     """Check Python 3 compatibility for a file with Python 2"""
     with open(f, 'rb') as fh:
@@ -55,7 +65,9 @@
     # out module paths for things not in a package can be confusing.
     if f.startswith(('hgext/', 'mercurial/')) and not f.endswith('__init__.py'):
         assert f.endswith('.py')
-        name = f.replace('/', '.')[:-3].replace('.pure.', '.')
+        name = f.replace('/', '.')[:-3]
+        if f.endswith(_dualmodules):
+            name = name.replace('.pure.', '.')
         try:
             importlib.import_module(name)
         except Exception as e: