diff --git a/Source/kwsys/testProcess.c b/Source/kwsys/testProcess.c
index 0060c4d1f..60449175b 100644
--- a/Source/kwsys/testProcess.c
+++ b/Source/kwsys/testProcess.c
@@ -94,7 +94,12 @@ int test4(int argc, const char* argv[])
   fprintf(stderr, "Output before crash on stderr from crash test.\n");  
   fflush(stdout);
   fflush(stderr);
+#if defined(__APPLE__) && defined(__x86_64__) && defined(__OPTIMIZE__) \
+ && defined(__clang__)
+  *(int*)1 = 0; /* Clang's optimizer produces bad code for 0-ptr.  */
+#else
   *(int*)0 = 0;
+#endif
   fprintf(stdout, "Output after crash on stdout from crash test.\n");
   fprintf(stderr, "Output after crash on stderr from crash test.\n");
   return 0;