diff --git a/bitbake/lib/bb/ui/knotty.py b/bitbake/lib/bb/ui/knotty.py
index 042b79e4b0..053d1e978b 100644
--- a/bitbake/lib/bb/ui/knotty.py
+++ b/bitbake/lib/bb/ui/knotty.py
@@ -533,10 +533,12 @@ def main(server, eventHandler, params, tf = TerminalFilter):
             main.shutdown = main.shutdown + 1
             pass
         except Exception as e:
-            sys.stderr.write(str(e))
+            import traceback
+            sys.stderr.write(traceback.format_exc())
             if not params.observe_only:
                 _, error = server.runCommand(["stateForceShutdown"])
             main.shutdown = 2
+            return_value = 1
     try:
         summary = ""
         if taskfailures: