diff --git a/object-store.h b/object-store.h
index 12415e5ea7..cfe47c9c07 100644
--- a/object-store.h
+++ b/object-store.h
@@ -110,7 +110,7 @@ struct packed_git {
 	const void *index_data;
 	size_t index_size;
 	uint32_t num_objects;
-	uint32_t crc_offset;
+	size_t crc_offset;
 	struct oidset bad_objects;
 	int index_version;
 	time_t mtime;
diff --git a/packfile.c b/packfile.c
index 5ee67de569..efe4a22c63 100644
--- a/packfile.c
+++ b/packfile.c
@@ -186,7 +186,7 @@ int load_idx(const char *path, const unsigned int hashsz, void *idx_map,
 		     */
 		    (sizeof(off_t) <= 4))
 			return error("pack too large for current definition of off_t in %s", path);
-		p->crc_offset = 8 + 4 * 256 + nr * hashsz;
+		p->crc_offset = st_add(8 + 4 * 256, st_mult(nr, hashsz));
 	}
 
 	p->index_version = version;