diff --git a/hgext/rebase.py b/hgext/rebase.py
--- a/hgext/rebase.py
+++ b/hgext/rebase.py
@@ -1791,7 +1791,7 @@
# But our merge base candidates (D and E in above case) could still be
# better than the default (ancestor(F, Z) == null). Therefore still
# pick one (so choose p1 above).
- if sum(1 for b in bases if b != nullrev) > 1:
+ if sum(1 for b in set(bases) if b != nullrev) > 1:
unwanted = [None, None] # unwanted[i]: unwanted revs if choose bases[i]
for i, base in enumerate(bases):
if base == nullrev: