diff --git a/runtests.py b/runtests.py
index b46c92736..322bd8ddb 100644
--- a/runtests.py
+++ b/runtests.py
@@ -28,8 +28,11 @@
               '/usr/local/lib/ccache', '/usr/local/lib/f90cache']
 
 # ---------------------------------------------------------------------
+if __doc__ is None:
+    __doc__ = "Run without -OO if you want usage info"
+else:
+    __doc__ = __doc__.format(**globals())
 
-__doc__ = __doc__.format(**globals())
 
 import sys
 import os