diff --git a/Documentation/git-check-ref-format.txt b/Documentation/git-check-ref-format.txt
index 171b68377d..c1ce26884e 100644
--- a/Documentation/git-check-ref-format.txt
+++ b/Documentation/git-check-ref-format.txt
@@ -7,7 +7,9 @@ git-check-ref-format - Ensures that a reference name is well formed
 
 SYNOPSIS
 --------
+[verse]
 'git check-ref-format' <refname>
+'git check-ref-format' [--branch] <branchname-shorthand>
 
 DESCRIPTION
 -----------
@@ -30,7 +32,11 @@ imposes the following rules on how references are named:
   caret `{caret}`, colon `:`, question-mark `?`, asterisk `*`,
   or open bracket `[` anywhere.
 
-. They cannot end with a slash `/`.
+. They cannot end with a slash `/` nor a dot `.`.
+
+. They cannot end with the sequence `.lock`.
+
+. They cannot contain a sequence `@{`.
 
 These rules make it easy for shell script based tools to parse
 reference names, pathname expansion by the shell when a reference name is used
@@ -49,6 +55,18 @@ reference name expressions (see linkgit:git-rev-parse[1]):
   It may also be used to select a specific object such as with
   'git-cat-file': "git cat-file blob v1.3.3:refs.c".
 
+. at-open-brace `@{` is used as a notation to access a reflog entry.
+
+With the `--branch` option, it expands a branch name shorthand and
+prints the name of the branch the shorthand refers to.
+
+EXAMPLE
+-------
+
+git check-ref-format --branch @{-1}::
+
+Print the name of the previous branch.
+
 
 GIT
 ---
diff --git a/branch.c b/branch.c
index 5f889fee6b..62030af4b5 100644
--- a/branch.c
+++ b/branch.c
@@ -134,16 +134,8 @@ void create_branch(const char *head,
 	char *real_ref, msg[PATH_MAX + 20];
 	struct strbuf ref = STRBUF_INIT;
 	int forcing = 0;
-	int len;
 
-	len = strlen(name);
-	if (interpret_nth_last_branch(name, &ref) != len) {
-		strbuf_reset(&ref);
-		strbuf_add(&ref, name, len);
-	}
-	strbuf_splice(&ref, 0, 0, "refs/heads/", 11);
-
-	if (check_ref_format(ref.buf))
+	if (strbuf_check_branch_ref(&ref, name))
 		die("'%s' is not a valid branch name.", name);
 
 	if (resolve_ref(ref.buf, sha1, 1, NULL)) {
diff --git a/builtin-branch.c b/builtin-branch.c
index 07a440eeba..ca81d725cb 100644
--- a/builtin-branch.c
+++ b/builtin-branch.c
@@ -121,11 +121,7 @@ static int delete_branches(int argc, const char **argv, int force, int kinds)
 			die("Couldn't look up commit object for HEAD");
 	}
 	for (i = 0; i < argc; i++, strbuf_release(&bname)) {
-		int len = strlen(argv[i]);
-
-		if (interpret_nth_last_branch(argv[i], &bname) != len)
-			strbuf_add(&bname, argv[i], len);
-
+		strbuf_branchname(&bname, argv[i]);
 		if (kinds == REF_LOCAL_BRANCH && !strcmp(head, bname.buf)) {
 			error("Cannot delete the branch '%s' "
 			      "which you are currently on.", bname.buf);
@@ -468,22 +464,27 @@ static void rename_branch(const char *oldname, const char *newname, int force)
 	struct strbuf oldref = STRBUF_INIT, newref = STRBUF_INIT, logmsg = STRBUF_INIT;
 	unsigned char sha1[20];
 	struct strbuf oldsection = STRBUF_INIT, newsection = STRBUF_INIT;
+	int recovery = 0;
 
 	if (!oldname)
 		die("cannot rename the current branch while not on any.");
 
-	strbuf_addf(&oldref, "refs/heads/%s", oldname);
+	if (strbuf_check_branch_ref(&oldref, oldname)) {
+		/*
+		 * Bad name --- this could be an attempt to rename a
+		 * ref that we used to allow to be created by accident.
+		 */
+		if (resolve_ref(oldref.buf, sha1, 1, NULL))
+			recovery = 1;
+		else
+			die("Invalid branch name: '%s'", oldname);
+	}
 
-	if (check_ref_format(oldref.buf))
-		die("Invalid branch name: %s", oldref.buf);
-
-	strbuf_addf(&newref, "refs/heads/%s", newname);
-
-	if (check_ref_format(newref.buf))
-		die("Invalid branch name: %s", newref.buf);
+	if (strbuf_check_branch_ref(&newref, newname))
+		die("Invalid branch name: '%s'", newname);
 
 	if (resolve_ref(newref.buf, sha1, 1, NULL) && !force)
-		die("A branch named '%s' already exists.", newname);
+		die("A branch named '%s' already exists.", newref.buf + 11);
 
 	strbuf_addf(&logmsg, "Branch: renamed %s to %s",
 		 oldref.buf, newref.buf);
@@ -492,6 +493,9 @@ static void rename_branch(const char *oldname, const char *newname, int force)
 		die("Branch rename failed");
 	strbuf_release(&logmsg);
 
+	if (recovery)
+		warning("Renamed a misnamed branch '%s' away", oldref.buf + 11);
+
 	/* no need to pass logmsg here as HEAD didn't really move */
 	if (!strcmp(oldname, head) && create_symref("HEAD", newref.buf, NULL))
 		die("Branch renamed to %s, but HEAD is not updated!", newname);
diff --git a/builtin-check-ref-format.c b/builtin-check-ref-format.c
index 701de439ae..f9381e07ea 100644
--- a/builtin-check-ref-format.c
+++ b/builtin-check-ref-format.c
@@ -5,9 +5,18 @@
 #include "cache.h"
 #include "refs.h"
 #include "builtin.h"
+#include "strbuf.h"
 
 int cmd_check_ref_format(int argc, const char **argv, const char *prefix)
 {
+	if (argc == 3 && !strcmp(argv[1], "--branch")) {
+		struct strbuf sb = STRBUF_INIT;
+
+		if (strbuf_check_branch_ref(&sb, argv[2]))
+			die("'%s' is not a valid branch name", argv[2]);
+		printf("%s\n", sb.buf + 11);
+		exit(0);
+	}
 	if (argc != 2)
 		usage("git check-ref-format refname");
 	return !!check_ref_format(argv[1]);
diff --git a/builtin-checkout.c b/builtin-checkout.c
index fc55bbe14d..33d1fecb62 100644
--- a/builtin-checkout.c
+++ b/builtin-checkout.c
@@ -353,16 +353,11 @@ struct branch_info {
 static void setup_branch_path(struct branch_info *branch)
 {
 	struct strbuf buf = STRBUF_INIT;
-	int ret;
 
-	if ((ret = interpret_nth_last_branch(branch->name, &buf))
-	    && ret == strlen(branch->name)) {
+	strbuf_branchname(&buf, branch->name);
+	if (strcmp(buf.buf, branch->name))
 		branch->name = xstrdup(buf.buf);
-		strbuf_splice(&buf, 0, 0, "refs/heads/", 11);
-	} else {
-		strbuf_addstr(&buf, "refs/heads/");
-		strbuf_addstr(&buf, branch->name);
-	}
+	strbuf_splice(&buf, 0, 0, "refs/heads/", 11);
 	branch->path = strbuf_detach(&buf, NULL);
 }
 
@@ -738,12 +733,11 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 
 	if (opts.new_branch) {
 		struct strbuf buf = STRBUF_INIT;
-		strbuf_addstr(&buf, "refs/heads/");
-		strbuf_addstr(&buf, opts.new_branch);
+		if (strbuf_check_branch_ref(&buf, opts.new_branch))
+			die("git checkout: we do not like '%s' as a branch name.",
+			    opts.new_branch);
 		if (!get_sha1(buf.buf, rev))
 			die("git checkout: branch %s already exists", opts.new_branch);
-		if (check_ref_format(buf.buf))
-			die("git checkout: we do not like '%s' as a branch name.", opts.new_branch);
 		strbuf_release(&buf);
 	}
 
diff --git a/builtin-merge.c b/builtin-merge.c
index 4c119359e7..6a51823a55 100644
--- a/builtin-merge.c
+++ b/builtin-merge.c
@@ -360,9 +360,8 @@ static void merge_name(const char *remote, struct strbuf *msg)
 	const char *ptr;
 	int len, early;
 
-	len = strlen(remote);
-	if (interpret_nth_last_branch(remote, &bname) == len)
-		remote = bname.buf;
+	strbuf_branchname(&bname, remote);
+	remote = bname.buf;
 
 	memset(branch_head, 0, sizeof(branch_head));
 	remote_head = peel_to_type(remote, 0, NULL, OBJ_COMMIT);
diff --git a/cache.h b/cache.h
index 61664addd7..ab1294d6fb 100644
--- a/cache.h
+++ b/cache.h
@@ -680,7 +680,7 @@ extern int read_ref(const char *filename, unsigned char *sha1);
 extern const char *resolve_ref(const char *path, unsigned char *sha1, int, int *);
 extern int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref);
 extern int dwim_log(const char *str, int len, unsigned char *sha1, char **ref);
-extern int interpret_nth_last_branch(const char *str, struct strbuf *);
+extern int interpret_branch_name(const char *str, struct strbuf *);
 
 extern int refname_match(const char *abbrev_name, const char *full_name, const char **rules);
 extern const char *ref_rev_parse_rules[];
diff --git a/refs.c b/refs.c
index 26b001453b..59c373fc6d 100644
--- a/refs.c
+++ b/refs.c
@@ -676,6 +676,7 @@ int for_each_rawref(each_ref_fn fn, void *cb_data)
  * - it has double dots "..", or
  * - it has ASCII control character, "~", "^", ":" or SP, anywhere, or
  * - it ends with a "/".
+ * - it ends with ".lock"
  */
 
 static inline int bad_ref_char(int ch)
@@ -693,7 +694,7 @@ static inline int bad_ref_char(int ch)
 
 int check_ref_format(const char *ref)
 {
-	int ch, level, bad_type;
+	int ch, level, bad_type, last;
 	int ret = CHECK_REF_FORMAT_OK;
 	const char *cp = ref;
 
@@ -717,21 +718,28 @@ int check_ref_format(const char *ref)
 				return CHECK_REF_FORMAT_ERROR;
 		}
 
+		last = ch;
 		/* scan the rest of the path component */
 		while ((ch = *cp++) != 0) {
 			bad_type = bad_ref_char(ch);
-			if (bad_type) {
+			if (bad_type)
 				return CHECK_REF_FORMAT_ERROR;
-			}
 			if (ch == '/')
 				break;
-			if (ch == '.' && *cp == '.')
+			if (last == '.' && ch == '.')
 				return CHECK_REF_FORMAT_ERROR;
+			if (last == '@' && ch == '{')
+				return CHECK_REF_FORMAT_ERROR;
+			last = ch;
 		}
 		level++;
 		if (!ch) {
+			if (ref <= cp - 2 && cp[-2] == '.')
+				return CHECK_REF_FORMAT_ERROR;
 			if (level < 2)
 				return CHECK_REF_FORMAT_ONELEVEL;
+			if (has_extension(ref, ".lock"))
+				return CHECK_REF_FORMAT_ERROR;
 			return ret;
 		}
 	}
diff --git a/sha1_name.c b/sha1_name.c
index 2f75179f4c..904bcd96a5 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -242,10 +242,10 @@ static int ambiguous_path(const char *path, int len)
  * *string and *len will only be substituted, and *string returned (for
  * later free()ing) if the string passed in is of the form @{-<n>}.
  */
-static char *substitute_nth_last_branch(const char **string, int *len)
+static char *substitute_branch_name(const char **string, int *len)
 {
 	struct strbuf buf = STRBUF_INIT;
-	int ret = interpret_nth_last_branch(*string, &buf);
+	int ret = interpret_branch_name(*string, &buf);
 
 	if (ret == *len) {
 		size_t size;
@@ -259,7 +259,7 @@ static char *substitute_nth_last_branch(const char **string, int *len)
 
 int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref)
 {
-	char *last_branch = substitute_nth_last_branch(&str, &len);
+	char *last_branch = substitute_branch_name(&str, &len);
 	const char **p, *r;
 	int refs_found = 0;
 
@@ -288,7 +288,7 @@ int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref)
 
 int dwim_log(const char *str, int len, unsigned char *sha1, char **log)
 {
-	char *last_branch = substitute_nth_last_branch(&str, &len);
+	char *last_branch = substitute_branch_name(&str, &len);
 	const char **p;
 	int logs_found = 0;
 
@@ -355,7 +355,7 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 		struct strbuf buf = STRBUF_INIT;
 		int ret;
 		/* try the @{-N} syntax for n-th checkout */
-		ret = interpret_nth_last_branch(str+at, &buf);
+		ret = interpret_branch_name(str+at, &buf);
 		if (ret > 0) {
 			/* substitute this branch name and restart */
 			return get_sha1_1(buf.buf, buf.len, sha1);
@@ -750,7 +750,7 @@ static int grab_nth_branch_switch(unsigned char *osha1, unsigned char *nsha1,
  * If the input was ok but there are not N branch switches in the
  * reflog, it returns 0.
  */
-int interpret_nth_last_branch(const char *name, struct strbuf *buf)
+int interpret_branch_name(const char *name, struct strbuf *buf)
 {
 	long nth;
 	int i, retval;
diff --git a/strbuf.c b/strbuf.c
index bfbd81632e..a88496030b 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -1,4 +1,5 @@
 #include "cache.h"
+#include "refs.h"
 
 int prefixcmp(const char *str, const char *prefix)
 {
@@ -357,3 +358,19 @@ int strbuf_read_file(struct strbuf *sb, const char *path, size_t hint)
 
 	return len;
 }
+
+int strbuf_branchname(struct strbuf *sb, const char *name)
+{
+	int len = strlen(name);
+	if (interpret_branch_name(name, sb) == len)
+		return 0;
+	strbuf_add(sb, name, len);
+	return len;
+}
+
+int strbuf_check_branch_ref(struct strbuf *sb, const char *name)
+{
+	strbuf_branchname(sb, name);
+	strbuf_splice(sb, 0, 0, "refs/heads/", 11);
+	return check_ref_format(sb->buf);
+}
diff --git a/strbuf.h b/strbuf.h
index 89bd36e15a..9ee908a3ec 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -131,4 +131,7 @@ extern int strbuf_getline(struct strbuf *, FILE *, int);
 extern void stripspace(struct strbuf *buf, int skip_comments);
 extern int launch_editor(const char *path, struct strbuf *buffer, const char *const *env);
 
+extern int strbuf_branchname(struct strbuf *sb, const char *name);
+extern int strbuf_check_branch_ref(struct strbuf *sb, const char *name);
+
 #endif /* STRBUF_H */