diff --git a/mercurial/branchmap.py b/mercurial/branchmap.py
--- a/mercurial/branchmap.py
+++ b/mercurial/branchmap.py
@@ -175,6 +175,10 @@
     def iteritems(self):
         return self.entries.iteritems()
 
+    def hasbranch(self, label):
+        """ checks whether a branch of this name exists or not """
+        return label in self.entries
+
     @classmethod
     def fromfile(cls, repo):
         f = None
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -1556,7 +1556,7 @@
         return scmutil.revsymbol(self, key).node()
 
     def lookupbranch(self, key):
-        if key in self.branchmap().entries:
+        if self.branchmap().hasbranch(key):
             return key
 
         return scmutil.revsymbol(self, key).branch()
@@ -2730,7 +2730,7 @@
         if branch is None:
             branch = self[None].branch()
         branches = self.branchmap()
-        if branch not in branches.entries:
+        if not branches.hasbranch(branch):
             return []
         # the cache returns heads ordered lowest to highest
         bheads = list(reversed(branches.branchheads(branch, closed=closed)))