diff --git a/t/t6300-for-each-ref.sh b/t/t6300-for-each-ref.sh
index 0d2e062f79..80679d5e12 100755
--- a/t/t6300-for-each-ref.sh
+++ b/t/t6300-for-each-ref.sh
@@ -59,18 +59,25 @@ test_atom() {
 	# Automatically test "contents:size" atom after testing "contents"
 	if test "$2" = "contents"
 	then
-		case $(git cat-file -t "$ref") in
-		tag)
-			# We cannot use $3 as it expects sanitize_pgp to run
-			expect=$(git cat-file tag $ref | tail -n +6 | wc -c) ;;
-		tree | blob)
-			expect='' ;;
-		commit)
-			expect=$(printf '%s' "$3" | wc -c) ;;
-		esac
-		# Leave $expect unquoted to lose possible leading whitespaces
-		echo $expect >expected
+		# for commit leg, $3 is changed there
+		expect=$(printf '%s' "$3" | wc -c)
 		test_expect_${4:-success} $PREREQ "basic atom: $1 contents:size" '
+			type=$(git cat-file -t "$ref") &&
+			case $type in
+			tag)
+				# We cannot use $3 as it expects sanitize_pgp to run
+				git cat-file tag $ref >out &&
+				expect=$(tail -n +6 out | wc -c) &&
+				rm -f out ;;
+			tree | blob)
+				expect="" ;;
+			commit)
+				: "use the calculated expect" ;;
+			*)
+				BUG "unknown object type" ;;
+			esac &&
+			# Leave $expect unquoted to lose possible leading whitespaces
+			echo $expect >expected &&
 			git for-each-ref --format="%(contents:size)" "$ref" >actual &&
 			test_cmp expected actual
 		'