diff --git a/course/versioning.py b/course/versioning.py
index ff4888f0a6e2c1b6e2f5b030524b43973a045197..30751b726fe561c46e9a87a34e6a7cce92f58918 100644
--- a/course/versioning.py
+++ b/course/versioning.py
@@ -73,7 +73,7 @@ def transfer_remote_refs(repo, remote_refs):
     for ref, sha in six.iteritems(remote_refs):
         if (ref.startswith(b"refs/heads/")
                 and not ref.startswith(b"refs/heads/origin/")):
-            new_ref = "refs/remotes/origin/"+_remove_prefix(b"refs/heads/", ref)
+            new_ref = b"refs/remotes/origin/"+_remove_prefix(b"refs/heads/", ref)
             valid_refs.append(new_ref)
             repo[new_ref] = sha
     for ref in repo.get_refs().keys():
@@ -188,6 +188,13 @@ class CourseCreationForm(StyledModelForm):
         self.helper.add_input(
                 Submit("submit", _("Validate and create")))
 
+    def clean_git_source(self):
+        if not self.cleaned_data["git_source"]:
+            from django.forms import ValidationError as FormValidationError
+            raise FormValidationError(_("Git source must be specified"))
+
+        return self.cleaned_data["git_source"]
+
 
 @login_required
 def set_up_new_course(request):