diff --git a/refs.c b/refs.c
index 096b42c5e993193dd83a02128be4b90ebc59edd1..832a52f7818369bca969d49317718714a5bcabac 100644
--- a/refs.c
+++ b/refs.c
@@ -56,6 +56,8 @@ static struct ref_list *add_ref(const char *name, const unsigned char *sha1,
 	entry = xmalloc(sizeof(struct ref_list) + len);
 	hashcpy(entry->sha1, sha1);
 	hashclr(entry->peeled);
+	if (check_refname_format(name, REFNAME_ALLOW_ONELEVEL|REFNAME_DOT_COMPONENT))
+		die("Reference has invalid format: '%s'", name);
 	memcpy(entry->name, name, len);
 	entry->flag = flag;
 	entry->next = list;
@@ -900,7 +902,7 @@ static inline int bad_ref_char(int ch)
  * the length of the component found, or -1 if the component is not
  * legal.
  */
-static int check_refname_component(const char *ref)
+static int check_refname_component(const char *ref, int flags)
 {
 	const char *cp;
 	char last = '\0';
@@ -919,8 +921,16 @@ static int check_refname_component(const char *ref)
 	}
 	if (cp == ref)
 		return -1; /* Component has zero length. */
-	if (ref[0] == '.')
-		return -1; /* Component starts with '.'. */
+	if (ref[0] == '.') {
+		if (!(flags & REFNAME_DOT_COMPONENT))
+			return -1; /* Component starts with '.'. */
+		/*
+		 * Even if leading dots are allowed, don't allow "."
+		 * as a component (".." is prevented by a rule above).
+		 */
+		if (ref[1] == '\0')
+			return -1; /* Component equals ".". */
+	}
 	if (cp - ref >= 5 && !memcmp(cp - 5, ".lock", 5))
 		return -1; /* Refname ends with ".lock". */
 	return cp - ref;
@@ -932,7 +942,7 @@ int check_refname_format(const char *ref, int flags)
 
 	while (1) {
 		/* We are at the start of a path component. */
-		component_len = check_refname_component(ref);
+		component_len = check_refname_component(ref, flags);
 		if (component_len < 0) {
 			if ((flags & REFNAME_REFSPEC_PATTERN) &&
 					ref[0] == '*' &&
diff --git a/refs.h b/refs.h
index b0da5fc95dff025a8dd5c1f299ee25efc6141e81..d5ac133336dc0da45cd916207d12a5e0e4237ae3 100644
--- a/refs.h
+++ b/refs.h
@@ -99,6 +99,7 @@ extern int for_each_reflog(each_ref_fn, void *);
 
 #define REFNAME_ALLOW_ONELEVEL 1
 #define REFNAME_REFSPEC_PATTERN 2
+#define REFNAME_DOT_COMPONENT 4
 
 /*
  * Return 0 iff ref has the correct format for a refname according to
@@ -106,7 +107,10 @@ extern int for_each_reflog(each_ref_fn, void *);
  * REFNAME_ALLOW_ONELEVEL is set in flags, then accept one-level
  * reference names.  If REFNAME_REFSPEC_PATTERN is set in flags, then
  * allow a "*" wildcard character in place of one of the name
- * components.  No leading or repeated slashes are accepted.
+ * components.  No leading or repeated slashes are accepted.  If
+ * REFNAME_DOT_COMPONENT is set in flags, then allow refname
+ * components to start with "." (but not a whole component equal to
+ * "." or "..").
  */
 extern int check_refname_format(const char *ref, int flags);