diff --git a/project.py b/project.py
index 95403cc..e501cc2 100644
--- a/project.py
+++ b/project.py
@@ -1730,10 +1730,11 @@
     if depth:
       current_branch_only = True
 
+    if ID_RE.match(self.revisionExpr) is not None:
+      is_sha1 = True
+
     if current_branch_only:
-      if ID_RE.match(self.revisionExpr) is not None:
-        is_sha1 = True
-      elif self.revisionExpr.startswith(R_TAGS):
+      if self.revisionExpr.startswith(R_TAGS):
         # this is a tag and its sha1 value should never change
         tag_name = self.revisionExpr[len(R_TAGS):]
 
@@ -1820,9 +1821,10 @@
       branch = self.revisionExpr
       if is_sha1:
         branch = self.upstream
-      if branch.startswith(R_HEADS):
-        branch = branch[len(R_HEADS):]
-      spec.append(str((u'+refs/heads/%s:' % branch) + remote.ToLocal('refs/heads/%s' % branch)))
+      if branch is not None and branch.strip():
+        if not branch.startswith('refs/'):
+          branch = R_HEADS + branch
+        spec.append(str((u'+%s:' % branch) + remote.ToLocal(branch)))
     cmd.extend(spec)
 
     shallowfetch = self.config.GetString('repo.shallowfetch')