diff --git a/pack-bitmap.c b/pack-bitmap.c
index 87f3b5cf4d..e84211de15 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -54,6 +54,16 @@ struct bitmap_index {
 	struct packed_git *pack;
 	struct multi_pack_index *midx;
 
+	/*
+	 * If using a multi-pack index chain, 'base' points to the
+	 * bitmap index corresponding to this bitmap's midx->base_midx.
+	 *
+	 * base_nr indicates how many layers precede this one, and is
+	 * zero when base is NULL.
+	 */
+	struct bitmap_index *base;
+	uint32_t base_nr;
+
 	/* mmapped buffer of the whole bitmap index */
 	unsigned char *map;
 	size_t map_size; /* size of the mmaped buffer */
@@ -386,8 +396,15 @@ static int load_bitmap_entries_v1(struct bitmap_index *index)
 char *midx_bitmap_filename(struct multi_pack_index *midx)
 {
 	struct strbuf buf = STRBUF_INIT;
-	get_midx_filename_ext(midx->repo->hash_algo, &buf, midx->object_dir,
-			      get_midx_checksum(midx), MIDX_EXT_BITMAP);
+	if (midx->has_chain)
+		get_split_midx_filename_ext(midx->repo->hash_algo, &buf,
+					    midx->object_dir,
+					    get_midx_checksum(midx),
+					    MIDX_EXT_BITMAP);
+	else
+		get_midx_filename_ext(midx->repo->hash_algo, &buf,
+				      midx->object_dir, get_midx_checksum(midx),
+				      MIDX_EXT_BITMAP);
 
 	return strbuf_detach(&buf, NULL);
 }
@@ -454,16 +471,21 @@ static int open_midx_bitmap_1(struct bitmap_index *bitmap_git,
 		goto cleanup;
 	}
 
-	for (i = 0; i < bitmap_git->midx->num_packs; i++) {
-		if (prepare_midx_pack(bitmap_repo(bitmap_git),
-				      bitmap_git->midx,
-				      i)) {
+	for (i = 0; i < bitmap_git->midx->num_packs + bitmap_git->midx->num_packs_in_base; i++) {
+		if (prepare_midx_pack(bitmap_repo(bitmap_git), bitmap_git->midx, i)) {
 			warning(_("could not open pack %s"),
 				bitmap_git->midx->pack_names[i]);
 			goto cleanup;
 		}
 	}
 
+	if (midx->base_midx) {
+		bitmap_git->base = prepare_midx_bitmap_git(midx->base_midx);
+		bitmap_git->base_nr = bitmap_git->base->base_nr + 1;
+	} else {
+		bitmap_git->base_nr = 0;
+	}
+
 	return 0;
 
 cleanup:
@@ -515,6 +537,7 @@ static int open_pack_bitmap_1(struct bitmap_index *bitmap_git, struct packed_git
 	bitmap_git->map_size = xsize_t(st.st_size);
 	bitmap_git->map = xmmap(NULL, bitmap_git->map_size, PROT_READ, MAP_PRIVATE, fd, 0);
 	bitmap_git->map_pos = 0;
+	bitmap_git->base_nr = 0;
 	close(fd);
 
 	if (load_bitmap_header(bitmap_git) < 0) {
@@ -534,8 +557,7 @@ static int open_pack_bitmap_1(struct bitmap_index *bitmap_git, struct packed_git
 static int load_reverse_index(struct repository *r, struct bitmap_index *bitmap_git)
 {
 	if (bitmap_is_midx(bitmap_git)) {
-		uint32_t i;
-		int ret;
+		struct multi_pack_index *m;
 
 		/*
 		 * The multi-pack-index's .rev file is already loaded via
@@ -544,10 +566,15 @@ static int load_reverse_index(struct repository *r, struct bitmap_index *bitmap_
 		 * But we still need to open the individual pack .rev files,
 		 * since we will need to make use of them in pack-objects.
 		 */
-		for (i = 0; i < bitmap_git->midx->num_packs; i++) {
-			ret = load_pack_revindex(r, bitmap_git->midx->packs[i]);
-			if (ret)
-				return ret;
+		for (m = bitmap_git->midx; m; m = m->base_midx) {
+			uint32_t i;
+			int ret;
+
+			for (i = 0; i < m->num_packs; i++) {
+				ret = load_pack_revindex(r, m->packs[i]);
+				if (ret)
+					return ret;
+			}
 		}
 		return 0;
 	}
@@ -573,6 +600,13 @@ static int load_bitmap(struct repository *r, struct bitmap_index *bitmap_git)
 	if (!bitmap_git->table_lookup && load_bitmap_entries_v1(bitmap_git) < 0)
 		goto failed;
 
+	if (bitmap_git->base) {
+		if (!bitmap_is_midx(bitmap_git))
+			BUG("non-MIDX bitmap has non-NULL base bitmap index");
+		if (load_bitmap(r, bitmap_git->base) < 0)
+			goto failed;
+	}
+
 	return 0;
 
 failed:
@@ -657,10 +691,9 @@ struct bitmap_index *prepare_bitmap_git(struct repository *r)
 
 struct bitmap_index *prepare_midx_bitmap_git(struct multi_pack_index *midx)
 {
-	struct repository *r = midx->repo;
 	struct bitmap_index *bitmap_git = xcalloc(1, sizeof(*bitmap_git));
 
-	if (!open_midx_bitmap_1(bitmap_git, midx) && !load_bitmap(r, bitmap_git))
+	if (!open_midx_bitmap_1(bitmap_git, midx))
 		return bitmap_git;
 
 	free_bitmap_index(bitmap_git);
@@ -2901,6 +2934,7 @@ void free_bitmap_index(struct bitmap_index *b)
 		close_midx_revindex(b->midx);
 	}
 	free_pseudo_merge_map(&b->pseudo_merges);
+	free_bitmap_index(b->base);
 	free(b);
 }