diff --git a/bin/git-up b/bin/git-up
index cfcc3b9..ed2d8ee 100755
--- a/bin/git-up
+++ b/bin/git-up
@@ -2,5 +2,12 @@
 
 set -e
 
-git fetch origin
-git rebase origin/master "$@"
+if git symbolic-ref --short refs/remotes/origin/HEAD >/dev/null; then
+  git rebase "$(git symbolic-ref --short refs/remotes/origin/HEAD | sed 's@^origin/@@')" "$@"
+else
+  echo "You don't have a primary branch reference set for your origin remote.
+Use:
+git symbolic-ref refs/remotes/origin/HEAD refs/remotes/origin/{name_of_your_primary_branch}
+
+to set the reference and then try rebasing again."
+fi