diff --git a/Lib/contextlib.py b/Lib/contextlib.py
index 4f83ef6..dbd1c57 100644
--- a/Lib/contextlib.py
+++ b/Lib/contextlib.py
@@ -25,6 +25,10 @@
             else:
                 raise RuntimeError("generator didn't stop")
         else:
+            if value is None:
+                # Need to force instantiation so we can reliably
+                # tell if we get the same exception back
+                value = type()
             try:
                 self.gen.throw(type, value, traceback)
                 raise RuntimeError("generator didn't stop after throw()")