diff --git a/packfile.c b/packfile.c
index efe4a22c63..70837b0d26 100644
--- a/packfile.c
+++ b/packfile.c
@@ -1948,14 +1948,15 @@ off_t nth_packed_object_offset(const struct packed_git *p, uint32_t n)
 	const unsigned int hashsz = the_hash_algo->rawsz;
 	index += 4 * 256;
 	if (p->index_version == 1) {
-		return ntohl(*((uint32_t *)(index + (hashsz + 4) * (size_t)n)));
+		return ntohl(*((uint32_t *)(index + st_mult(hashsz + 4, n))));
 	} else {
 		uint32_t off;
-		index += 8 + (size_t)p->num_objects * (hashsz + 4);
-		off = ntohl(*((uint32_t *)(index + 4 * n)));
+		index += st_add(8, st_mult(p->num_objects, hashsz + 4));
+		off = ntohl(*((uint32_t *)(index + st_mult(4, n))));
 		if (!(off & 0x80000000))
 			return off;
-		index += (size_t)p->num_objects * 4 + (off & 0x7fffffff) * 8;
+		index += st_add(st_mult(p->num_objects, 4),
+				st_mult(off & 0x7fffffff, 8));
 		check_pack_index_ptr(p, index);
 		return get_be64(index);
 	}