diff --git a/pack-bitmap-write.c b/pack-bitmap-write.c
index 4fcfaed428..9b1be59f6d 100644
--- a/pack-bitmap-write.c
+++ b/pack-bitmap-write.c
@@ -650,20 +650,15 @@ static const struct object_id *oid_access(size_t pos, const void *table)
 
 static void write_selected_commits_v1(struct hashfile *f,
 				      struct pack_idx_entry **index,
-				      uint32_t index_nr)
+				      uint32_t index_nr,
+				      uint32_t *commit_positions)
 {
 	int i;
 
 	for (i = 0; i < writer.selected_nr; ++i) {
 		struct bitmapped_commit *stored = &writer.selected[i];
 
-		int commit_pos =
-			oid_pos(&stored->commit->object.oid, index, index_nr, oid_access);
-
-		if (commit_pos < 0)
-			BUG("trying to write commit not in index");
-
-		hashwrite_be32(f, commit_pos);
+		hashwrite_be32(f, commit_positions[i]);
 		hashwrite_u8(f, stored->xor_offset);
 		hashwrite_u8(f, stored->flags);
 
@@ -697,6 +692,8 @@ void bitmap_writer_finish(struct pack_idx_entry **index,
 	static uint16_t flags = BITMAP_OPT_FULL_DAG;
 	struct strbuf tmp_file = STRBUF_INIT;
 	struct hashfile *f;
+	uint32_t *commit_positions = NULL;
+	uint32_t i;
 
 	struct bitmap_disk_header header;
 
@@ -715,7 +712,20 @@ void bitmap_writer_finish(struct pack_idx_entry **index,
 	dump_bitmap(f, writer.trees);
 	dump_bitmap(f, writer.blobs);
 	dump_bitmap(f, writer.tags);
-	write_selected_commits_v1(f, index, index_nr);
+
+	ALLOC_ARRAY(commit_positions, writer.selected_nr);
+
+	for (i = 0; i < writer.selected_nr; i++) {
+		struct bitmapped_commit *stored = &writer.selected[i];
+		int commit_pos = oid_pos(&stored->commit->object.oid, index, index_nr, oid_access);
+
+		if (commit_pos < 0)
+			BUG(_("trying to write commit not in index"));
+
+		commit_positions[i] = commit_pos;
+	}
+
+	write_selected_commits_v1(f, index, index_nr, commit_positions);
 
 	if (options & BITMAP_OPT_HASH_CACHE)
 		write_hash_cache(f, index, index_nr);
@@ -730,4 +740,5 @@ void bitmap_writer_finish(struct pack_idx_entry **index,
 		die_errno("unable to rename temporary bitmap file to '%s'", filename);
 
 	strbuf_release(&tmp_file);
+	free(commit_positions);
 }