diff --git a/builtin/fast-import.c b/builtin/fast-import.c
index 82bc6dcc00..3dff898c43 100644
--- a/builtin/fast-import.c
+++ b/builtin/fast-import.c

@@ -1239,6 +1239,8 @@ static void *gfi_unpack_entry(
 	unsigned long *sizep)
 {
 	enum object_type type;
+	size_t size_st = 0;
+	void *data;
 	struct packed_git *p = all_packs[oe->pack_id];
 	if (p == pack_data && p->pack_size < (pack_size + the_hash_algo->rawsz)) {
 		/* The object is stored in the packfile we are writing to

@@ -1260,7 +1262,10 @@ static void *gfi_unpack_entry(
 		 */
 		p->pack_size = pack_size + the_hash_algo->rawsz;
 	}
-	return unpack_entry(the_repository, p, oe->idx.offset, &type, sizep);
+	data = unpack_entry(the_repository, p, oe->idx.offset, &type, &size_st);
+	if (sizep)
+		*sizep = cast_size_t_to_ulong(size_st);
+	return data;
 }