diff --git a/t/t1503-rev-parse-verify.sh b/t/t1503-rev-parse-verify.sh
index 100f857b16..813cc1b3e2 100755
--- a/t/t1503-rev-parse-verify.sh
+++ b/t/t1503-rev-parse-verify.sh
@@ -106,8 +106,8 @@ test_expect_success 'use --default' '
 
 test_expect_success 'master@{n} for various n' '
 	N=$(git reflog | wc -l) &&
-	Nm1=$((N-1)) &&
-	Np1=$((N+1)) &&
+	Nm1=$(($N-1)) &&
+	Np1=$(($N+1)) &&
 	git rev-parse --verify master@{0} &&
 	git rev-parse --verify master@{1} &&
 	git rev-parse --verify master@{$Nm1} &&