diff --git a/diff.c b/diff.c
index d24f47df99..ace4a1d387 100644
--- a/diff.c
+++ b/diff.c
@@ -4115,6 +4115,9 @@ void diff_free_filespec_blob(struct diff_filespec *s)
 
 void diff_free_filespec_data(struct diff_filespec *s)
 {
+	if (!s)
+		return;
+
 	diff_free_filespec_blob(s);
 	FREE_AND_NULL(s->cnt_data);
 }
diff --git a/t/t7800-difftool.sh b/t/t7800-difftool.sh
index 524f30f7dc..a578b35761 100755
--- a/t/t7800-difftool.sh
+++ b/t/t7800-difftool.sh
@@ -728,6 +728,19 @@ test_expect_success 'add -N and difftool -d' '
 	git difftool --dir-diff --extcmd ls
 '
 
+test_expect_success 'difftool --cached with unmerged files' '
+	test_when_finished git reset --hard &&
+
+	test_commit conflicting &&
+	test_commit conflict-a conflict.t a &&
+	git reset --hard conflicting &&
+	test_commit conflict-b conflict.t b &&
+	test_must_fail git merge conflict-a &&
+
+	git difftool --cached --no-prompt >output &&
+	test_must_be_empty output
+'
+
 test_expect_success 'outside worktree' '
 	echo 1 >1 &&
 	echo 2 >2 &&