diff --git a/builtin/commit.c b/builtin/commit.c
index cb73857..50bacd6 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -257,8 +257,9 @@
 	m = xcalloc(1, i);
 
 	if (with_tree) {
-		const char *max_prefix = pathspec_prefix(prefix, pattern);
-		overlay_tree_on_cache(with_tree, max_prefix);
+		char *max_prefix = pathspec_prefix(pattern);
+		overlay_tree_on_cache(with_tree, max_prefix ? max_prefix : prefix);
+		free(max_prefix);
 	}
 
 	for (i = 0; i < active_nr; i++) {