diff --git a/tools/clean.py b/tools/clean.py
index 92de461a3..66ab6cc1c 100644
--- a/tools/clean.py
+++ b/tools/clean.py
@@ -18,7 +18,15 @@ Only really intended to be used by internal build scripts.
 """
 
 import os
+import sys
+
 try:
     os.remove("pymongo/_cbson.so")
 except:
     pass
+
+try:
+    from pymongo import _cbson
+    sys.exit("could still import _cbson")
+except ImportError:
+    pass