diff --git a/git_common.py b/git_common.py
index 91ddeb4..e9b3220 100644
--- a/git_common.py
+++ b/git_common.py
@@ -530,7 +530,11 @@
   parent = parent or upstream(branch)
   if parent is None or branch is None:
     return None
-  actual_merge_base = run('merge-base', parent, branch)
+
+  try:
+    actual_merge_base = run('merge-base', '--fork-point', parent, branch)
+  except subprocess2.CalledProcessError:
+    actual_merge_base = run('merge-base', parent, branch)
 
   if base_upstream != parent:
     base = None