diff --git a/mitogen/master.py b/mitogen/master.py
index 3a163a8b0..4fb535f0a 100644
--- a/mitogen/master.py
+++ b/mitogen/master.py
@@ -536,7 +536,7 @@ def find(self, fullname):
 
         try:
             path = loader.get_filename(fullname)
-        except (AttributeError, ImportError):
+        except (AttributeError, ImportError, ValueError):
             # - get_filename() may throw ImportError if pkgutil.find_loader()
             #   picks a "parent" package's loader for some crap that's been
             #   stuffed in sys.modules, for example in the case of urllib3: