diff --git a/obs/update_unstable.py b/obs/update_unstable.py
index f3378fb..636898c 100755
--- a/obs/update_unstable.py
+++ b/obs/update_unstable.py
@@ -45,7 +45,8 @@ def project_exists(project: str) -> bool:
 def get_remote_hash(url: str, branch: str = "master") -> str:
 
     gitcmd = git.cmd.Git()
-    revision = gitcmd.ls_remote(url, branch, quiet=True, refs=True)
+    revision = gitcmd.ls_remote(url, f"refs/heads/{branch}",
+                                quiet=True, refs=True)
     git_hash, branch = revision.split("\t")
     return git_hash