diff --git a/src/applications/diffusion/engine/DiffusionCommitHookEngine.php b/src/applications/diffusion/engine/DiffusionCommitHookEngine.php
--- a/src/applications/diffusion/engine/DiffusionCommitHookEngine.php
+++ b/src/applications/diffusion/engine/DiffusionCommitHookEngine.php
@@ -760,10 +760,15 @@
         // repository that's already full of garbage (strongly discouraged but
         // not as inherently dangerous). These cases should be very uncommon.
 
+        // NOTE: We're only looking for heads on the same branch. The old
+        // tip of the branch may be the branchpoint for other branches, but that
+        // is OK.
+
         $dfutures = array();
         foreach ($old_heads as $old_head) {
           $dfutures[$old_head] = $repository->getLocalCommandFuture(
-            'log --rev %s --template %s',
+            'log --branch %s --rev %s --template %s',
+            $ref,
             hgsprintf('(descendants(%s) and head())', $old_head),
             '{node}\1');
         }