diff --git a/buildbot_nix/__init__.py b/buildbot_nix/__init__.py
index b27998d..6cdd62b 100644
--- a/buildbot_nix/__init__.py
+++ b/buildbot_nix/__init__.py
@@ -347,7 +347,8 @@ class NixEvalCommand(buildstep.ShellMixin, steps.BuildStep):
         # run nix-eval-jobs --flake .#$FLAKE_TARGET_ATTRIBUTE_FOR_JOBS to generate the dict of stages
         cmd: remotecommand.RemoteCommand = yield self.makeRemoteShellCommand()
         build_props = self.build.getProperties()
-        project_name = build_props.getProperty('event.project')
+        project_name = build_props.getProperty('event.refUpdate.project')
+        assert project_name is not None, "`event.refUpdate.project` is not available on the build properties, unexpected build type!"
 
         yield self.runCommand(cmd)