diff -r 65f2c92ed079 Lib/test/test_signal.py
--- a/Lib/test/test_signal.py	Sun Jul 07 23:30:24 2013 +0200
+++ b/Lib/test/test_signal.py	Mon Jul 08 00:34:32 2013 -0600
@@ -209,8 +209,10 @@
         for sig in (signal.SIGABRT, signal.SIGBREAK, signal.SIGFPE,
                     signal.SIGILL, signal.SIGINT, signal.SIGSEGV,
                     signal.SIGTERM):
-            # Set and then reset a handler for signals that work on windows
-            signal.signal(sig, signal.signal(sig, handler))
+            # Set and then reset a handler for signals that work on windows.
+            # Issue #18396, only for signals without a C-level handler.
+            if signal.getsignal(sig) is not None:
+                signal.signal(sig, signal.signal(sig, handler))
 
         with self.assertRaises(ValueError):
             signal.signal(-1, handler)