diff --git a/git-submodule.sh b/git-submodule.sh
index 9aa57dd..5a9d3c0 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -561,6 +561,7 @@
 	then
 		# before the first commit: compare with an empty tree
 		head=$(git hash-object -w -t tree --stdin </dev/null)
+		test -z "$1" || shift
 	else
 		head="HEAD"
 	fi