diff --git a/mkosi.images/system/mkosi.sync b/mkosi.images/system/mkosi.sync
index 517b7c9346..d56ddf5790 100755
--- a/mkosi.images/system/mkosi.sync
+++ b/mkosi.images/system/mkosi.sync
@@ -15,7 +15,7 @@ if [[ -d "$PKG_SUBDIR/.git" ]]; then
     fi
 
     # If work is being done on the packaging rules in a separate branch, don't touch the checkout.
-    if ! git merge-base --is-ancestor HEAD "origin/$GIT_BRANCH"; then
+    if ! git -C "$PKG_SUBDIR" merge-base --is-ancestor HEAD "origin/$GIT_BRANCH"; then
         EXIT_STATUS=$?
         if [[ $EXIT_STATUS -eq 1 ]]; then
             exit 0