diff --git a/mercurial/tags.py b/mercurial/tags.py
--- a/mercurial/tags.py
+++ b/mercurial/tags.py
@@ -244,7 +244,7 @@
 
     # remove tags pointing to invalid nodes
     cl = repo.changelog
-    for t in filetags.keys():
+    for t in list(filetags):
         try:
             cl.rev(filetags[t][0])
         except (LookupError, ValueError):