diff --git a/pretty.c b/pretty.c
index 3c43db558ae..fe249f8820f 100644
--- a/pretty.c
+++ b/pretty.c
@@ -1267,6 +1267,8 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 			if (c->signature_check.key)
 				strbuf_addstr(sb, c->signature_check.key);
 			break;
+		default:
+			return 0;
 		}
 		return 2;
 	}
diff --git a/t/t7510-signed-commit.sh b/t/t7510-signed-commit.sh
index e97477a3b98..9810242435b 100755
--- a/t/t7510-signed-commit.sh
+++ b/t/t7510-signed-commit.sh
@@ -147,4 +147,10 @@ test_expect_success GPG 'show lack of signature with custom format' '
 	test_cmp expect actual
 '
 
+test_expect_success 'unused %G placeholders are passed through' '
+	echo "%GX %G" >expect &&
+	git log -1 --format="%GX %G" >actual &&
+	test_cmp expect actual
+'
+
 test_done