diff --git a/autoninja.py b/autoninja.py
index a00ec81693..3a958fbc3d 100755
--- a/autoninja.py
+++ b/autoninja.py
@@ -336,6 +336,13 @@ def _main_inner(input_args, build_id, should_collect_logs=False):
                         ] + input_args[1:],
                         should_collect_logs)
                 return siso.main(["siso", "ninja"] + input_args[1:])
+            if not project:
+                project = _siso_rbe_project()
+            if not t_specified and project and not offline:
+                print(
+                    'Missing "use_remoteexec=true". No remote execution',
+                    file=sys.stderr,
+                )
             return siso.main(["siso", "ninja", "--offline"] + input_args[1:])
 
         if os.path.exists(siso_marker):