diff --git a/revision.c b/revision.c
index c4390f0938..b5db2d764a 100644
--- a/revision.c
+++ b/revision.c
@@ -2068,6 +2068,7 @@ static void prepare_show_merge(struct rev_info *revs)
 	parse_pathspec(&revs->prune_data, PATHSPEC_ALL_MAGIC & ~PATHSPEC_LITERAL,
 		       PATHSPEC_PREFER_FULL | PATHSPEC_LITERAL_PATH, "", prune);
 	revs->limited = 1;
+	free(prune);
 }
 
 static int dotdot_missing(const char *arg, char *dotdot,
diff --git a/t/t7007-show.sh b/t/t7007-show.sh
index d6cc69e0f2..2d322b53d1 100755
--- a/t/t7007-show.sh
+++ b/t/t7007-show.sh
@@ -167,4 +167,28 @@ test_expect_success 'show --graph is forbidden' '
   test_must_fail git show --graph HEAD
 '
 
+test_expect_success 'show unmerged index' '
+	git reset --hard &&
+
+	git switch -C base &&
+	echo "base" >conflicting &&
+	git add conflicting &&
+	git commit -m "base" &&
+
+	git branch hello &&
+	git branch goodbye &&
+
+	git switch hello &&
+	echo "hello" >conflicting &&
+	git commit -am "hello" &&
+
+	git switch goodbye &&
+	echo "goodbye" >conflicting &&
+	git commit -am "goodbye" &&
+
+	git switch hello &&
+	test_must_fail git merge goodbye &&
+	git show --merge HEAD
+'
+
 test_done