diff --git a/ci/nur/manifest.py b/ci/nur/manifest.py
index 346e819b6..215e0b176 100644
--- a/ci/nur/manifest.py
+++ b/ci/nur/manifest.py
@@ -67,10 +67,7 @@ class Repo:
             self.file = "default.nix"
         else:
             self.file = file_
-        if branch is None:
-            self.branch = "master"
-        else:
-            self.branch = branch
+        self.branch = branch
         self.locked_version = None
 
         if (
@@ -155,7 +152,7 @@ def load_manifest(manifest_path: PathType, lock_path: PathType) -> Manifest:
     for name, repo in data["repos"].items():
         url = urlparse(repo["url"])
         submodules = repo.get("submodules", False)
-        branch_ = repo.get("branch", "master")
+        branch_ = repo.get("branch")
         file_ = repo.get("file", "default.nix")
         type_ = repo.get("type", None)
         locked_version = locked_versions.get(name)
diff --git a/ci/nur/prefetch.py b/ci/nur/prefetch.py
index 56b321a2a..31313d791 100644
--- a/ci/nur/prefetch.py
+++ b/ci/nur/prefetch.py
@@ -26,7 +26,7 @@ class GitPrefetcher:
 
     def latest_commit(self) -> str:
         data = subprocess.check_output(
-            ["git", "ls-remote", self.repo.url.geturl(), self.repo.branch],
+            ["git", "ls-remote", self.repo.url.geturl(), self.repo.branch or "HEAD"],
             env={**os.environ, "GIT_ASKPASS": "", "GIT_TERMINAL_PROMPT": "0"},
         )
         return data.decode().split(maxsplit=1)[0]
@@ -35,7 +35,8 @@ class GitPrefetcher:
         cmd = ["nix-prefetch-git"]
         if self.repo.submodules:
             cmd += ["--fetch-submodules"]
-        cmd += ["--rev", f"refs/heads/{self.repo.branch}"]
+        if self.repo.branch:
+            cmd += ["--rev", f"refs/heads/{self.repo.branch}"]
         cmd += [self.repo.url.geturl()]
         proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
         try: