patch4161.diff

diff --git a/numba/funcdesc.py b/numba/funcdesc.py
index 740e43e93..77b583543 100644
--- a/numba/funcdesc.py
+++ b/numba/funcdesc.py
@@ -145,7 +145,7 @@ class FunctionDescriptor(object):
         kws = ()        # TODO
         global_dict = None
 
-        if modname is None:
+        if modname is None or modname not in sys.modules:
             # Dynamically generated function.
             modname = _dynamic_modname
             # Retain a reference to the dictionary of the function.