diff --git a/buildbot_nix/buildbot_nix/__init__.py b/buildbot_nix/buildbot_nix/__init__.py
index 0272e4b92..1446625d0 100644
--- a/buildbot_nix/buildbot_nix/__init__.py
+++ b/buildbot_nix/buildbot_nix/__init__.py
@@ -237,6 +237,7 @@ def set_common_properties(
         props.setProperty("virtual_builder_tags", "", source)
         props.setProperty("attr", job.attr, source)
         props.setProperty("combine_builds", combine_builds, source)
+        props.setProperty("default_branch", project.default_branch, source)
 
         if isinstance(job, NixEvalJobSuccess):
             props.setProperty("drv_path", job.drvPath, source)