diff --git a/submodule.c b/submodule.c
index 12a2503fda..540e9df485 100644
--- a/submodule.c
+++ b/submodule.c
@@ -2038,7 +2038,7 @@ const char *get_superproject_working_tree(void)
 		 * We're only interested in the name after the tab.
 		 */
 		super_sub = strchr(sb.buf, '\t') + 1;
-		super_sub_len = sb.buf + sb.len - super_sub - 1;
+		super_sub_len = strlen(super_sub);
 
 		if (super_sub_len > cwd_len ||
 		    strcmp(&cwd[cwd_len - super_sub_len], super_sub))
diff --git a/t/t1500-rev-parse.sh b/t/t1500-rev-parse.sh
index 5c715fe2cf..01abee533d 100755
--- a/t/t1500-rev-parse.sh
+++ b/t/t1500-rev-parse.sh
@@ -141,6 +141,22 @@ test_expect_success 'showing the superproject correctly' '
 	test_commit -C sub test_commit &&
 	git -C super submodule add ../sub dir/sub &&
 	echo $(pwd)/super >expect  &&
+	git -C super/dir/sub rev-parse --show-superproject-working-tree >out &&
+	test_cmp expect out &&
+
+	test_commit -C super submodule_add &&
+	git -C super checkout -b branch1 &&
+	git -C super/dir/sub checkout -b branch1 &&
+	test_commit -C super/dir/sub branch1_commit &&
+	git -C super add dir/sub &&
+	test_commit -C super branch1_commit &&
+	git -C super checkout -b branch2 master &&
+	git -C super/dir/sub checkout -b branch2 master &&
+	test_commit -C super/dir/sub branch2_commit &&
+	git -C super add dir/sub &&
+	test_commit -C super branch2_commit &&
+	test_must_fail git -C super merge branch1 &&
+
 	git -C super/dir/sub rev-parse --show-superproject-working-tree >out &&
 	test_cmp expect out
 '