diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 2c525cc1b2..a44e61ab0f 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -2955,9 +2955,9 @@ static unsigned int check_delta_limit(struct object_entry *me, unsigned int n)
 	return m;
 }
 
-static unsigned long free_unpacked(struct unpacked *n)
+static size_t free_unpacked(struct unpacked *n)
 {
-	unsigned long freed_mem = sizeof_delta_index(n->index);
+	size_t freed_mem = sizeof_delta_index(n->index);
 	free_delta_index(n->index);
 	n->index = NULL;
 	if (n->data) {