diff --git a/Documentation/git-cat-file.txt b/Documentation/git-cat-file.txt
index f82d702d6b..830f0a2eff 100644
--- a/Documentation/git-cat-file.txt
+++ b/Documentation/git-cat-file.txt
@@ -91,26 +91,49 @@ OPTIONS
 --batch::
 --batch=<format>::
 	Print object information and contents for each object provided
-	on stdin.  May not be combined with any other options or arguments
-	except `--textconv` or `--filters`, in which case the input lines
-	also need to specify the path, separated by whitespace.  See the
-	section `BATCH OUTPUT` below for details.
+	on stdin. May not be combined with any other options or arguments
+	except `--textconv`, `--filters`, or `--use-mailmap`.
+	+
+	* When used with `--textconv` or `--filters`, the input lines
+	  must specify the path, separated by whitespace. See the section
+	  `BATCH OUTPUT` below for details.
+	+
+	* When used with `--use-mailmap`, for commit and tag objects, the
+	  contents part of the output shows the identities replaced using the
+	  mailmap mechanism, while the information part of the output shows
+	  the size of the object as if it actually recorded the replacement
+	  identities.
 
 --batch-check::
 --batch-check=<format>::
-	Print object information for each object provided on stdin.  May
-	not be combined with any other options or arguments except
-	`--textconv` or `--filters`, in which case the input lines also
-	need to specify the path, separated by whitespace.  See the
-	section `BATCH OUTPUT` below for details.
+	Print object information for each object provided on stdin. May not be
+	combined with any other options or arguments except `--textconv`, `--filters`
+	or `--use-mailmap`.
+	+
+	* When used with `--textconv` or `--filters`, the input lines must
+	 specify the path, separated by whitespace. See the section
+	 `BATCH OUTPUT` below for details.
+	+
+	* When used with `--use-mailmap`, for commit and tag objects, the
+	  printed object information shows the size of the object as if the
+	  identities recorded in it were replaced by the mailmap mechanism.
 
 --batch-command::
 --batch-command=<format>::
 	Enter a command mode that reads commands and arguments from stdin. May
-	only be combined with `--buffer`, `--textconv` or `--filters`. In the
-	case of `--textconv` or `--filters`, the input lines also need to specify
-	the path, separated by whitespace. See the section `BATCH OUTPUT` below
-	for details.
+	only be combined with `--buffer`, `--textconv`, `--use-mailmap` or
+	`--filters`.
+	+
+	* When used with `--textconv` or `--filters`, the input lines must
+	  specify the path, separated by whitespace. See the section
+	  `BATCH OUTPUT` below for details.
+	+
+	* When used with `--use-mailmap`, for commit and tag objects, the
+	  `contents` command shows the identities replaced using the
+	  mailmap mechanism, while the `info` command shows the size
+	  of the object as if it actually recorded the replacement
+	  identities.
+
 +
 `--batch-command` recognizes the following commands:
 +
diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index dde8dbeacd..cc17635e76 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -444,6 +444,9 @@ static void batch_object_write(const char *obj_name,
 	if (!data->skip_object_info) {
 		int ret;
 
+		if (use_mailmap)
+			data->info.typep = &data->type;
+
 		if (pack)
 			ret = packed_object_info(the_repository, pack, offset,
 						 &data->info);
@@ -457,6 +460,18 @@ static void batch_object_write(const char *obj_name,
 			fflush(stdout);
 			return;
 		}
+
+		if (use_mailmap && (data->type == OBJ_COMMIT || data->type == OBJ_TAG)) {
+			size_t s = data->size;
+			char *buf = NULL;
+
+			buf = repo_read_object_file(the_repository, &data->oid, &data->type,
+						    &data->size);
+			buf = replace_idents_using_mailmap(buf, &s);
+			data->size = cast_size_t_to_ulong(s);
+
+			free(buf);
+		}
 	}
 
 	strbuf_reset(scratch);
diff --git a/t/t4203-mailmap.sh b/t/t4203-mailmap.sh
index b8ec5e0959..fa7f987284 100755
--- a/t/t4203-mailmap.sh
+++ b/t/t4203-mailmap.sh
@@ -1051,4 +1051,40 @@ test_expect_success 'git cat-file -s returns correct size with --use-mailmap for
 	test_cmp expect actual
 '
 
+test_expect_success 'git cat-file --batch-check returns correct size with --use-mailmap' '
+	test_when_finished "rm .mailmap" &&
+	cat >.mailmap <<-\EOF &&
+	C O Mitter <committer@example.com> Orig <orig@example.com>
+	EOF
+	git cat-file commit HEAD >commit.out &&
+	commit_size=$(wc -c <commit.out) &&
+	commit_sha=$(git rev-parse HEAD) &&
+	echo $commit_sha commit $commit_size >expect &&
+	git cat-file --use-mailmap commit HEAD >commit.out &&
+	commit_size=$(wc -c <commit.out) &&
+	echo $commit_sha commit $commit_size >>expect &&
+	echo "HEAD" >in &&
+	git cat-file --batch-check <in >actual &&
+	git cat-file --use-mailmap --batch-check <in >>actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'git cat-file --batch-command returns correct size with --use-mailmap' '
+	test_when_finished "rm .mailmap" &&
+	cat >.mailmap <<-\EOF &&
+	C O Mitter <committer@example.com> Orig <orig@example.com>
+	EOF
+	git cat-file commit HEAD >commit.out &&
+	commit_size=$(wc -c <commit.out) &&
+	commit_sha=$(git rev-parse HEAD) &&
+	echo $commit_sha commit $commit_size >expect &&
+	git cat-file --use-mailmap commit HEAD >commit.out &&
+	commit_size=$(wc -c <commit.out) &&
+	echo $commit_sha commit $commit_size >>expect &&
+	echo "info HEAD" >in &&
+	git cat-file --batch-command <in >actual &&
+	git cat-file --use-mailmap --batch-command <in >>actual &&
+	test_cmp expect actual
+'
+
 test_done
