diff --git a/builtin/fsck.c b/builtin/fsck.c
index 0928a98a71..e9ba576c1f 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -298,7 +298,7 @@ static int fsck_obj(struct object *obj)
 
 	if (fsck_walk(obj, mark_used, NULL))
 		objerror(obj, "broken links");
-	if (fsck_object(obj, check_strict, fsck_error_func))
+	if (fsck_object(obj, NULL, 0, check_strict, fsck_error_func))
 		return -1;
 
 	if (obj->type == OBJ_TREE) {
diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index eebf1a8fc2..f89df017c2 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -779,7 +779,8 @@ static void sha1_object(const void *data, struct object_entry *obj_entry,
 			if (!obj)
 				die(_("invalid %s"), typename(type));
 			if (do_fsck_object &&
-			    fsck_object(obj, 1, fsck_error_function))
+			    fsck_object(obj, buf, size, 1,
+				    fsck_error_function))
 				die(_("Error in object"));
 			if (fsck_walk(obj, mark_link, NULL))
 				die(_("Not all child objects of %s are reachable"), sha1_to_hex(obj->sha1));
diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c
index 99cde45879..855d94b90b 100644
--- a/builtin/unpack-objects.c
+++ b/builtin/unpack-objects.c
@@ -164,10 +164,10 @@ static unsigned nr_objects;
  * Called only from check_object() after it verified this object
  * is Ok.
  */
-static void write_cached_object(struct object *obj)
+static void write_cached_object(struct object *obj, struct obj_buffer *obj_buf)
 {
 	unsigned char sha1[20];
-	struct obj_buffer *obj_buf = lookup_object_buffer(obj);
+
 	if (write_sha1_file(obj_buf->buffer, obj_buf->size, typename(obj->type), sha1) < 0)
 		die("failed to write object %s", sha1_to_hex(obj->sha1));
 	obj->flags |= FLAG_WRITTEN;
@@ -180,6 +180,8 @@ static void write_cached_object(struct object *obj)
  */
 static int check_object(struct object *obj, int type, void *data)
 {
+	struct obj_buffer *obj_buf;
+
 	if (!obj)
 		return 1;
 
@@ -198,11 +200,15 @@ static int check_object(struct object *obj, int type, void *data)
 		return 0;
 	}
 
-	if (fsck_object(obj, 1, fsck_error_function))
+	obj_buf = lookup_object_buffer(obj);
+	if (!obj_buf)
+		die("Whoops! Cannot find object '%s'", sha1_to_hex(obj->sha1));
+	if (fsck_object(obj, obj_buf->buffer, obj_buf->size, 1,
+			fsck_error_function))
 		die("Error in object");
 	if (fsck_walk(obj, check_object, NULL))
 		die("Error on reachable objects of %s", sha1_to_hex(obj->sha1));
-	write_cached_object(obj);
+	write_cached_object(obj, obj_buf);
 	return 0;
 }
 
diff --git a/fsck.c b/fsck.c
index 56156fff44..2fffa434a5 100644
--- a/fsck.c
+++ b/fsck.c
@@ -6,6 +6,7 @@
 #include "commit.h"
 #include "tag.h"
 #include "fsck.h"
+#include "refs.h"
 
 static int fsck_walk_tree(struct tree *tree, fsck_walk_func walk, void *data)
 {
@@ -237,6 +238,26 @@ static int fsck_tree(struct tree *item, int strict, fsck_error error_func)
 	return retval;
 }
 
+static int require_end_of_header(const void *data, unsigned long size,
+	struct object *obj, fsck_error error_func)
+{
+	const char *buffer = (const char *)data;
+	unsigned long i;
+
+	for (i = 0; i < size; i++) {
+		switch (buffer[i]) {
+		case '\0':
+			return error_func(obj, FSCK_ERROR,
+				"unterminated header: NUL at offset %d", i);
+		case '\n':
+			if (i + 1 < size && buffer[i + 1] == '\n')
+				return 0;
+		}
+	}
+
+	return error_func(obj, FSCK_ERROR, "unterminated header");
+}
+
 static int fsck_ident(const char **ident, struct object *obj, fsck_error error_func)
 {
 	char *end;
@@ -277,13 +298,16 @@ static int fsck_ident(const char **ident, struct object *obj, fsck_error error_f
 }
 
 static int fsck_commit_buffer(struct commit *commit, const char *buffer,
-			      fsck_error error_func)
+	unsigned long size, fsck_error error_func)
 {
 	unsigned char tree_sha1[20], sha1[20];
 	struct commit_graft *graft;
 	unsigned parent_count, parent_line_count = 0;
 	int err;
 
+	if (require_end_of_header(buffer, size, &commit->object, error_func))
+		return -1;
+
 	if (!skip_prefix(buffer, "tree ", &buffer))
 		return error_func(&commit->object, FSCK_ERROR, "invalid format - expected 'tree' line");
 	if (get_sha1_hex(buffer, tree_sha1) || buffer[40] != '\n')
@@ -322,24 +346,111 @@ static int fsck_commit_buffer(struct commit *commit, const char *buffer,
 	return 0;
 }
 
-static int fsck_commit(struct commit *commit, fsck_error error_func)
+static int fsck_commit(struct commit *commit, const char *data,
+	unsigned long size, fsck_error error_func)
 {
-	const char *buffer = get_commit_buffer(commit, NULL);
-	int ret = fsck_commit_buffer(commit, buffer, error_func);
-	unuse_commit_buffer(commit, buffer);
+	const char *buffer = data ?  data : get_commit_buffer(commit, &size);
+	int ret = fsck_commit_buffer(commit, buffer, size, error_func);
+	if (!data)
+		unuse_commit_buffer(commit, buffer);
 	return ret;
 }
 
-static int fsck_tag(struct tag *tag, fsck_error error_func)
+static int fsck_tag_buffer(struct tag *tag, const char *data,
+	unsigned long size, fsck_error error_func)
+{
+	unsigned char sha1[20];
+	int ret = 0;
+	const char *buffer;
+	char *to_free = NULL, *eol;
+	struct strbuf sb = STRBUF_INIT;
+
+	if (data)
+		buffer = data;
+	else {
+		enum object_type type;
+
+		buffer = to_free =
+			read_sha1_file(tag->object.sha1, &type, &size);
+		if (!buffer)
+			return error_func(&tag->object, FSCK_ERROR,
+				"cannot read tag object");
+
+		if (type != OBJ_TAG) {
+			ret = error_func(&tag->object, FSCK_ERROR,
+				"expected tag got %s",
+			    typename(type));
+			goto done;
+		}
+	}
+
+	if (require_end_of_header(buffer, size, &tag->object, error_func))
+		goto done;
+
+	if (!skip_prefix(buffer, "object ", &buffer)) {
+		ret = error_func(&tag->object, FSCK_ERROR, "invalid format - expected 'object' line");
+		goto done;
+	}
+	if (get_sha1_hex(buffer, sha1) || buffer[40] != '\n') {
+		ret = error_func(&tag->object, FSCK_ERROR, "invalid 'object' line format - bad sha1");
+		goto done;
+	}
+	buffer += 41;
+
+	if (!skip_prefix(buffer, "type ", &buffer)) {
+		ret = error_func(&tag->object, FSCK_ERROR, "invalid format - expected 'type' line");
+		goto done;
+	}
+	eol = strchr(buffer, '\n');
+	if (!eol) {
+		ret = error_func(&tag->object, FSCK_ERROR, "invalid format - unexpected end after 'type' line");
+		goto done;
+	}
+	if (type_from_string_gently(buffer, eol - buffer, 1) < 0)
+		ret = error_func(&tag->object, FSCK_ERROR, "invalid 'type' value");
+	if (ret)
+		goto done;
+	buffer = eol + 1;
+
+	if (!skip_prefix(buffer, "tag ", &buffer)) {
+		ret = error_func(&tag->object, FSCK_ERROR, "invalid format - expected 'tag' line");
+		goto done;
+	}
+	eol = strchr(buffer, '\n');
+	if (!eol) {
+		ret = error_func(&tag->object, FSCK_ERROR, "invalid format - unexpected end after 'type' line");
+		goto done;
+	}
+	strbuf_addf(&sb, "refs/tags/%.*s", (int)(eol - buffer), buffer);
+	if (check_refname_format(sb.buf, 0))
+		error_func(&tag->object, FSCK_WARN, "invalid 'tag' name: %s", buffer);
+	buffer = eol + 1;
+
+	if (!skip_prefix(buffer, "tagger ", &buffer))
+		/* early tags do not contain 'tagger' lines; warn only */
+		error_func(&tag->object, FSCK_WARN, "invalid format - expected 'tagger' line");
+	else
+		ret = fsck_ident(&buffer, &tag->object, error_func);
+
+done:
+	strbuf_release(&sb);
+	free(to_free);
+	return ret;
+}
+
+static int fsck_tag(struct tag *tag, const char *data,
+	unsigned long size, fsck_error error_func)
 {
 	struct object *tagged = tag->tagged;
 
 	if (!tagged)
 		return error_func(&tag->object, FSCK_ERROR, "could not load tagged object");
-	return 0;
+
+	return fsck_tag_buffer(tag, data, size, error_func);
 }
 
-int fsck_object(struct object *obj, int strict, fsck_error error_func)
+int fsck_object(struct object *obj, void *data, unsigned long size,
+	int strict, fsck_error error_func)
 {
 	if (!obj)
 		return error_func(obj, FSCK_ERROR, "no valid object to fsck");
@@ -349,9 +460,11 @@ int fsck_object(struct object *obj, int strict, fsck_error error_func)
 	if (obj->type == OBJ_TREE)
 		return fsck_tree((struct tree *) obj, strict, error_func);
 	if (obj->type == OBJ_COMMIT)
-		return fsck_commit((struct commit *) obj, error_func);
+		return fsck_commit((struct commit *) obj, (const char *) data,
+			size, error_func);
 	if (obj->type == OBJ_TAG)
-		return fsck_tag((struct tag *) obj, error_func);
+		return fsck_tag((struct tag *) obj, (const char *) data,
+			size, error_func);
 
 	return error_func(obj, FSCK_ERROR, "unknown type '%d' (internal fsck error)",
 			  obj->type);
diff --git a/fsck.h b/fsck.h
index 1e4f527318..d1e6387a44 100644
--- a/fsck.h
+++ b/fsck.h
@@ -28,6 +28,8 @@ int fsck_error_function(struct object *obj, int type, const char *fmt, ...);
  *    0		everything OK
  */
 int fsck_walk(struct object *obj, fsck_walk_func walk, void *data);
-int fsck_object(struct object *obj, int strict, fsck_error error_func);
+/* If NULL is passed for data, we assume the object is local and read it. */
+int fsck_object(struct object *obj, void *data, unsigned long size,
+	int strict, fsck_error error_func);
 
 #endif
diff --git a/object.c b/object.c
index a16b9f9e93..aedac243f0 100644
--- a/object.c
+++ b/object.c
@@ -33,13 +33,20 @@ const char *typename(unsigned int type)
 	return object_type_strings[type];
 }
 
-int type_from_string(const char *str)
+int type_from_string_gently(const char *str, ssize_t len, int gentle)
 {
 	int i;
 
+	if (len < 0)
+		len = strlen(str);
+
 	for (i = 1; i < ARRAY_SIZE(object_type_strings); i++)
-		if (!strcmp(str, object_type_strings[i]))
+		if (!strncmp(str, object_type_strings[i], len))
 			return i;
+
+	if (gentle)
+		return -1;
+
 	die("invalid object type \"%s\"", str);
 }
 
diff --git a/object.h b/object.h
index 5e8d8ee548..e028ced74c 100644
--- a/object.h
+++ b/object.h
@@ -53,7 +53,8 @@ struct object {
 };
 
 extern const char *typename(unsigned int type);
-extern int type_from_string(const char *str);
+extern int type_from_string_gently(const char *str, ssize_t, int gentle);
+#define type_from_string(str) type_from_string_gently(str, -1, 0)
 
 /*
  * Return the current number of buckets in the object hashmap.
diff --git a/t/t1450-fsck.sh b/t/t1450-fsck.sh
index b52397afd3..c23408ec07 100755
--- a/t/t1450-fsck.sh
+++ b/t/t1450-fsck.sh
@@ -214,6 +214,25 @@ test_expect_success 'tag pointing to something else than its type' '
 	test_must_fail git fsck --tags
 '
 
+test_expect_success 'tag with incorrect tag name & missing tagger' '
+	sha=$(git rev-parse HEAD) &&
+	cat >wrong-tag <<-EOF &&
+	object $sha
+	type commit
+	tag wrong name format
+
+	This is an invalid tag.
+	EOF
+
+	tag=$(git hash-object -t tag -w --stdin <wrong-tag) &&
+	test_when_finished "remove_object $tag" &&
+	echo $tag >.git/refs/tags/wrong &&
+	test_when_finished "git update-ref -d refs/tags/wrong" &&
+	git fsck --tags 2>out &&
+	grep "invalid .tag. name" out &&
+	grep "expected .tagger. line" out
+'
+
 test_expect_success 'cleaned up' '
 	git fsck >actual 2>&1 &&
 	test_cmp empty actual
diff --git a/t/t5302-pack-index.sh b/t/t5302-pack-index.sh
index 4bbb718751..61bc8da560 100755
--- a/t/t5302-pack-index.sh
+++ b/t/t5302-pack-index.sh
@@ -243,4 +243,23 @@ test_expect_success 'running index-pack in the object store' '
     test -f .git/objects/pack/pack-${pack1}.idx
 '
 
+test_expect_success 'index-pack --strict warns upon missing tagger in tag' '
+    sha=$(git rev-parse HEAD) &&
+    cat >wrong-tag <<EOF &&
+object $sha
+type commit
+tag guten tag
+
+This is an invalid tag.
+EOF
+
+    tag=$(git hash-object -t tag -w --stdin <wrong-tag) &&
+    pack1=$(echo $tag $sha | git pack-objects tag-test) &&
+    echo remove tag object &&
+    thirtyeight=${tag#??} &&
+    rm -f .git/objects/${tag%$thirtyeight}/$thirtyeight &&
+    git index-pack --strict tag-test-${pack1}.pack 2>err &&
+    grep "^error:.* expected .tagger. line" err
+'
+
 test_done