diff --git a/builtin-reset.c b/builtin-reset.c
index 5467e36c73..79792eebf2 100644
--- a/builtin-reset.c
+++ b/builtin-reset.c
@@ -46,26 +46,14 @@ static inline int is_merge(void)
 
 static int unmerged_files(void)
 {
-	char b;
-	ssize_t len;
-	struct child_process cmd;
-	const char *argv_ls_files[] = {"ls-files", "--unmerged", NULL};
-
-	memset(&cmd, 0, sizeof(cmd));
-	cmd.argv = argv_ls_files;
-	cmd.git_cmd = 1;
-	cmd.out = -1;
-
-	if (start_command(&cmd))
-		die("Could not run sub-command: git ls-files");
-
-	len = xread(cmd.out, &b, 1);
-	if (len < 0)
-		die("Could not read output from git ls-files: %s",
-						strerror(errno));
-	finish_command(&cmd);
-
-	return len;
+	int i;
+	read_cache();
+	for (i = 0; i < active_nr; i++) {
+		struct cache_entry *ce = active_cache[i];
+		if (ce_stage(ce))
+			return 1;
+	}
+	return 0;
 }
 
 static int reset_index_file(const unsigned char *sha1, int is_hard_reset)
diff --git a/t/t7102-reset.sh b/t/t7102-reset.sh
index cea9afb764..506767d2d7 100755
--- a/t/t7102-reset.sh
+++ b/t/t7102-reset.sh
@@ -59,6 +59,15 @@ test_expect_success 'giving a non existing revision should fail' '
 	check_changes 3ec39651e7f44ea531a5de18a9fa791c0fd370fc
 '
 
+test_expect_success 'reset --soft with unmerged index should fail' '
+	touch .git/MERGE_HEAD &&
+	echo "100644 44c5b5884550c17758737edcced463447b91d42b 1	un" |
+		git update-index --index-info &&
+	! git reset --soft HEAD &&
+	rm .git/MERGE_HEAD &&
+	git rm --cached -- un
+'
+
 test_expect_success \
 	'giving paths with options different than --mixed should fail' '
 	! git reset --soft -- first &&