diff --git a/Documentation/config/index.txt b/Documentation/config/index.txt
index 75f3a2d105..23c7985eb4 100644
--- a/Documentation/config/index.txt
+++ b/Documentation/config/index.txt
@@ -30,3 +30,14 @@ index.version::
 	Specify the version with which new index files should be
 	initialized.  This does not affect existing repositories.
 	If `feature.manyFiles` is enabled, then the default is 4.
+
+index.skipHash::
+	When enabled, do not compute the trailing hash for the index file.
+	This accelerates Git commands that manipulate the index, such as
+	`git add`, `git commit`, or `git status`. Instead of storing the
+	checksum, write a trailing set of bytes with value zero, indicating
+	that the computation was skipped.
++
+If you enable `index.skipHash`, then Git clients older than 2.13.0 will
+refuse to parse the index and Git clients older than 2.40.0 will report an
+error during `git fsck`.
diff --git a/read-cache.c b/read-cache.c
index 46f5e497b1..d73a81e41a 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1817,6 +1817,8 @@ static int verify_hdr(const struct cache_header *hdr, unsigned long size)
 	git_hash_ctx c;
 	unsigned char hash[GIT_MAX_RAWSZ];
 	int hdr_version;
+	unsigned char *start, *end;
+	struct object_id oid;
 
 	if (hdr->hdr_signature != htonl(CACHE_SIGNATURE))
 		return error(_("bad signature 0x%08x"), hdr->hdr_signature);
@@ -1827,10 +1829,16 @@ static int verify_hdr(const struct cache_header *hdr, unsigned long size)
 	if (!verify_index_checksum)
 		return 0;
 
+	end = (unsigned char *)hdr + size;
+	start = end - the_hash_algo->rawsz;
+	oidread(&oid, start);
+	if (oideq(&oid, null_oid()))
+		return 0;
+
 	the_hash_algo->init_fn(&c);
 	the_hash_algo->update_fn(&c, hdr, size - the_hash_algo->rawsz);
 	the_hash_algo->final_fn(hash, &c);
-	if (!hasheq(hash, (unsigned char *)hdr + size - the_hash_algo->rawsz))
+	if (!hasheq(hash, start))
 		return error(_("bad index file sha1 signature"));
 	return 0;
 }
@@ -2915,9 +2923,12 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 	int ieot_entries = 1;
 	struct index_entry_offset_table *ieot = NULL;
 	int nr, nr_threads;
+	struct repository *r = istate->repo ? istate->repo : the_repository;
 
 	f = hashfd(tempfile->fd, tempfile->filename.buf);
 
+	repo_config_get_bool(r, "index.skiphash", &f->skip_hash);
+
 	for (i = removed = extended = 0; i < entries; i++) {
 		if (cache[i]->ce_flags & CE_REMOVE)
 			removed++;
diff --git a/t/t1600-index.sh b/t/t1600-index.sh
index 010989f90e..98c5a83db7 100755
--- a/t/t1600-index.sh
+++ b/t/t1600-index.sh
@@ -65,6 +65,20 @@ test_expect_success 'out of bounds index.version issues warning' '
 	)
 '
 
+test_expect_success 'index.skipHash config option' '
+	rm -f .git/index &&
+	git -c index.skipHash=true add a &&
+	git fsck &&
+
+	test_commit start &&
+	git -c protocol.file.allow=always submodule add ./ sub &&
+	git config index.skipHash false &&
+	git -C sub config index.skipHash true &&
+	>sub/file &&
+	git -C sub add a &&
+	git -C sub fsck
+'
+
 test_index_version () {
 	INDEX_VERSION_CONFIG=$1 &&
 	FEATURE_MANY_FILES=$2 &&