diff --git a/setup.py b/setup.py
index 8e88750..751abff 100755
--- a/setup.py
+++ b/setup.py
@@ -88,7 +88,7 @@ else:
     macros = [("__LITTLE_ENDIAN__", "1")]
 
 ext_modules = []
-if not PYPY and not PY2:
+if not PYPY and not PY2 and not os.environ.get("MSGPACK_PUREPYTHON"):
     ext_modules.append(
         Extension(
             "msgpack._cmsgpack",