diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index bc35d8a80e5d03..e49fc1ebb45782 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -417,6 +417,9 @@ def add_handler(self, handler):
                 continue
 
             i = meth.find("_")
+            if i < 1:
+                # Don't match "open", "_open", etc.
+                continue
             protocol = meth[:i]
             condition = meth[i+1:]