diff --git a/Documentation/config.txt b/Documentation/config.txt
index 4b0c3682cc..499a3c4360 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1872,6 +1872,17 @@ pack.writebitmaps::
 	space and extra time spent on the initial repack.  Defaults to
 	false.
 
+pack.writeBitmapHashCache::
+	When true, git will include a "hash cache" section in the bitmap
+	index (if one is written). This cache can be used to feed git's
+	delta heuristics, potentially leading to better deltas between
+	bitmapped and non-bitmapped objects (e.g., when serving a fetch
+	between an older, bitmapped pack and objects that have been
+	pushed since the last gc). The downside is that it consumes 4
+	bytes per object of disk space, and that JGit's bitmap
+	implementation does not understand it, causing it to complain if
+	Git and JGit are used on the same repository. Defaults to false.
+
 pager.<cmd>::
 	If the value is boolean, turns on or off pagination of the
 	output of a particular Git subcommand when writing to a tty.
diff --git a/Documentation/technical/bitmap-format.txt b/Documentation/technical/bitmap-format.txt
index 7a86bd77d5..f8c18a0f7a 100644
--- a/Documentation/technical/bitmap-format.txt
+++ b/Documentation/technical/bitmap-format.txt
@@ -21,6 +21,12 @@ GIT bitmap v1 format
 			requirement for the bitmap index format, also present in JGit,
 			that greatly reduces the complexity of the implementation.
 
+			- BITMAP_OPT_HASH_CACHE (0x4)
+			If present, the end of the bitmap file contains
+			`N` 32-bit name-hash values, one per object in the
+			pack. The format and meaning of the name-hash is
+			described below.
+
 		4-byte entry count (network byte order)
 
 			The total count of entries (bitmapped commits) in this bitmap index.
@@ -129,3 +135,30 @@ The bitstream represented by the above chunk is then:
 The next word after `L_M` (if any) must again be a RLW, for the next
 chunk.  For efficient appending to the bitstream, the EWAH stores a
 pointer to the last RLW in the stream.
+
+
+== Appendix B: Optional Bitmap Sections
+
+These sections may or may not be present in the `.bitmap` file; their
+presence is indicated by the header flags section described above.
+
+Name-hash cache
+---------------
+
+If the BITMAP_OPT_HASH_CACHE flag is set, the end of the bitmap contains
+a cache of 32-bit values, one per object in the pack. The value at
+position `i` is the hash of the pathname at which the `i`th object
+(counting in index order) in the pack can be found.  This can be fed
+into the delta heuristics to compare objects with similar pathnames.
+
+The hash algorithm used is:
+
+    hash = 0;
+    while ((c = *name++))
+	    if (!isspace(c))
+		    hash = (hash >> 2) + (c << 24);
+
+Note that this hashing scheme is tied to the BITMAP_OPT_HASH_CACHE flag.
+If implementations want to choose a different hashing scheme, they are
+free to do so, but MUST allocate a new header flag (because comparing
+hashes made under two different schemes would be pointless).
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index fd6ae01ba4..fd741970e6 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -64,6 +64,7 @@ static off_t reuse_packfile_offset;
 
 static int use_bitmap_index = 1;
 static int write_bitmap_index;
+static uint16_t write_bitmap_options;
 
 static unsigned long delta_cache_size = 0;
 static unsigned long max_delta_cache_size = 256 * 1024 * 1024;
@@ -851,7 +852,8 @@ static void write_pack_file(void)
 				bitmap_writer_reuse_bitmaps(&to_pack);
 				bitmap_writer_select_commits(indexed_commits, indexed_commits_nr, -1);
 				bitmap_writer_build(&to_pack);
-				bitmap_writer_finish(written_list, nr_written, tmpname);
+				bitmap_writer_finish(written_list, nr_written,
+						     tmpname, write_bitmap_options);
 				write_bitmap_index = 0;
 			}
 
@@ -2201,6 +2203,12 @@ static int git_pack_config(const char *k, const char *v, void *cb)
 		write_bitmap_index = git_config_bool(k, v);
 		return 0;
 	}
+	if (!strcmp(k, "pack.writebitmaphashcache")) {
+		if (git_config_bool(k, v))
+			write_bitmap_options |= BITMAP_OPT_HASH_CACHE;
+		else
+			write_bitmap_options &= ~BITMAP_OPT_HASH_CACHE;
+	}
 	if (!strcmp(k, "pack.usebitmaps")) {
 		use_bitmap_index = git_config_bool(k, v);
 		return 0;
diff --git a/pack-bitmap-write.c b/pack-bitmap-write.c
index 954a74d6cf..1218befaf2 100644
--- a/pack-bitmap-write.c
+++ b/pack-bitmap-write.c
@@ -490,6 +490,19 @@ static void write_selected_commits_v1(struct sha1file *f,
 	}
 }
 
+static void write_hash_cache(struct sha1file *f,
+			     struct pack_idx_entry **index,
+			     uint32_t index_nr)
+{
+	uint32_t i;
+
+	for (i = 0; i < index_nr; ++i) {
+		struct object_entry *entry = (struct object_entry *)index[i];
+		uint32_t hash_value = htonl(entry->hash);
+		sha1write(f, &hash_value, sizeof(hash_value));
+	}
+}
+
 void bitmap_writer_set_checksum(unsigned char *sha1)
 {
 	hashcpy(writer.pack_checksum, sha1);
@@ -497,7 +510,8 @@ void bitmap_writer_set_checksum(unsigned char *sha1)
 
 void bitmap_writer_finish(struct pack_idx_entry **index,
 			  uint32_t index_nr,
-			  const char *filename)
+			  const char *filename,
+			  uint16_t options)
 {
 	static char tmp_file[PATH_MAX];
 	static uint16_t default_version = 1;
@@ -514,7 +528,7 @@ void bitmap_writer_finish(struct pack_idx_entry **index,
 
 	memcpy(header.magic, BITMAP_IDX_SIGNATURE, sizeof(BITMAP_IDX_SIGNATURE));
 	header.version = htons(default_version);
-	header.options = htons(flags);
+	header.options = htons(flags | options);
 	header.entry_count = htonl(writer.selected_nr);
 	memcpy(header.checksum, writer.pack_checksum, 20);
 
@@ -525,6 +539,9 @@ void bitmap_writer_finish(struct pack_idx_entry **index,
 	dump_bitmap(f, writer.tags);
 	write_selected_commits_v1(f, index, index_nr);
 
+	if (options & BITMAP_OPT_HASH_CACHE)
+		write_hash_cache(f, index, index_nr);
+
 	sha1close(f, NULL, CSUM_FSYNC);
 
 	if (adjust_shared_perm(tmp_file))
diff --git a/pack-bitmap.c b/pack-bitmap.c
index 82090a6741..ae0b57b950 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -66,6 +66,9 @@ static struct bitmap_index {
 	/* Number of bitmapped commits */
 	uint32_t entry_count;
 
+	/* Name-hash cache (or NULL if not present). */
+	uint32_t *hashes;
+
 	/*
 	 * Extended index.
 	 *
@@ -152,6 +155,11 @@ static int load_bitmap_header(struct bitmap_index *index)
 		if ((flags & BITMAP_OPT_FULL_DAG) == 0)
 			return error("Unsupported options for bitmap index file "
 				"(Git requires BITMAP_OPT_FULL_DAG)");
+
+		if (flags & BITMAP_OPT_HASH_CACHE) {
+			unsigned char *end = index->map + index->map_size - 20;
+			index->hashes = ((uint32_t *)end) - index->pack->num_objects;
+		}
 	}
 
 	index->entry_count = ntohl(header->entry_count);
@@ -626,6 +634,9 @@ static void show_objects_for_type(
 			entry = &bitmap_git.reverse_index->revindex[pos + offset];
 			sha1 = nth_packed_object_sha1(bitmap_git.pack, entry->nr);
 
+			if (bitmap_git.hashes)
+				hash = ntohl(bitmap_git.hashes[entry->nr]);
+
 			show_reach(sha1, object_type, 0, hash, bitmap_git.pack, entry->offset);
 		}
 
diff --git a/pack-bitmap.h b/pack-bitmap.h
index 09acf02f7b..8b7f4e9f0d 100644
--- a/pack-bitmap.h
+++ b/pack-bitmap.h
@@ -24,7 +24,8 @@ static const char BITMAP_IDX_SIGNATURE[] = {'B', 'I', 'T', 'M'};
 #define NEEDS_BITMAP (1u<<22)
 
 enum pack_bitmap_opts {
-	BITMAP_OPT_FULL_DAG = 1
+	BITMAP_OPT_FULL_DAG = 1,
+	BITMAP_OPT_HASH_CACHE = 4,
 };
 
 enum pack_bitmap_flags {
@@ -57,6 +58,7 @@ void bitmap_writer_select_commits(struct commit **indexed_commits,
 void bitmap_writer_build(struct packing_data *to_pack);
 void bitmap_writer_finish(struct pack_idx_entry **index,
 			  uint32_t index_nr,
-			  const char *filename);
+			  const char *filename,
+			  uint16_t options);
 
 #endif
diff --git a/t/perf/p5310-pack-bitmaps.sh b/t/perf/p5310-pack-bitmaps.sh
index 8c6ae4567c..685d46f8b7 100755
--- a/t/perf/p5310-pack-bitmaps.sh
+++ b/t/perf/p5310-pack-bitmaps.sh
@@ -9,7 +9,8 @@ test_perf_large_repo
 # since we want to be able to compare bitmap-aware
 # git versus non-bitmap git
 test_expect_success 'setup bitmap config' '
-	git config pack.writebitmaps true
+	git config pack.writebitmaps true &&
+	git config pack.writebitmaphashcache true
 '
 
 test_perf 'repack to disk' '
diff --git a/t/t5310-pack-bitmaps.sh b/t/t5310-pack-bitmaps.sh
index d2b0c45cca..d3a3afaba8 100755
--- a/t/t5310-pack-bitmaps.sh
+++ b/t/t5310-pack-bitmaps.sh
@@ -14,7 +14,8 @@ test_expect_success 'setup repo with moderate-sized history' '
 	git checkout master &&
 	blob=$(echo tagged-blob | git hash-object -w --stdin) &&
 	git tag tagged-blob $blob &&
-	git config pack.writebitmaps true
+	git config pack.writebitmaps true &&
+	git config pack.writebitmaphashcache true
 '
 
 test_expect_success 'full repack creates bitmaps' '