diff --git a/midx.c b/midx.c
index 6f07de3688..bc4797196f 100644
--- a/midx.c
+++ b/midx.c
@@ -25,13 +25,15 @@ const unsigned char *get_midx_checksum(struct multi_pack_index *m)
 
 void get_midx_filename(struct strbuf *out, const char *object_dir)
 {
-	strbuf_addf(out, "%s/pack/multi-pack-index", object_dir);
+	get_midx_filename_ext(out, object_dir, NULL, NULL);
 }
 
-void get_midx_rev_filename(struct strbuf *out, struct multi_pack_index *m)
+void get_midx_filename_ext(struct strbuf *out, const char *object_dir,
+			   const unsigned char *hash, const char *ext)
 {
-	get_midx_filename(out, m->object_dir);
-	strbuf_addf(out, "-%s.rev", hash_to_hex(get_midx_checksum(m)));
+	strbuf_addf(out, "%s/pack/multi-pack-index", object_dir);
+	if (ext)
+		strbuf_addf(out, "-%s.%s", hash_to_hex(hash), ext);
 }
 
 static int midx_read_oid_fanout(const unsigned char *chunk_start,
diff --git a/midx.h b/midx.h
index dc477dff44..8554f2d616 100644
--- a/midx.h
+++ b/midx.h
@@ -74,9 +74,13 @@ struct multi_pack_index {
 #define MIDX_WRITE_BITMAP_HASH_CACHE (1 << 3)
 #define MIDX_WRITE_BITMAP_LOOKUP_TABLE (1 << 4)
 
+#define MIDX_EXT_REV "rev"
+#define MIDX_EXT_BITMAP "bitmap"
+
 const unsigned char *get_midx_checksum(struct multi_pack_index *m);
 void get_midx_filename(struct strbuf *out, const char *object_dir);
-void get_midx_rev_filename(struct strbuf *out, struct multi_pack_index *m);
+void get_midx_filename_ext(struct strbuf *out, const char *object_dir,
+			   const unsigned char *hash, const char *ext);
 
 struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local);
 int prepare_midx_pack(struct repository *r, struct multi_pack_index *m, uint32_t pack_int_id);
diff --git a/pack-revindex.c b/pack-revindex.c
index a7624d8be8..fc63aa76a2 100644
--- a/pack-revindex.c
+++ b/pack-revindex.c
@@ -381,7 +381,8 @@ int load_midx_revindex(struct multi_pack_index *m)
 	trace2_data_string("load_midx_revindex", the_repository,
 			   "source", "rev");
 
-	get_midx_rev_filename(&revindex_name, m);
+	get_midx_filename_ext(&revindex_name, m->object_dir,
+			      get_midx_checksum(m), MIDX_EXT_REV);
 
 	ret = load_revindex_from_disk(revindex_name.buf,
 				      m->num_objects,