diff --git a/src/Debug/DebugHook.py b/src/Debug/DebugHook.py
index cfd97252..739d8e48 100644
--- a/src/Debug/DebugHook.py
+++ b/src/Debug/DebugHook.py
@@ -52,7 +52,12 @@ else:
 gevent.hub.Hub._original_handle_error = gevent.hub.Hub.handle_error
 
 def handleGreenletError(self, context, type, value, tb):
-    sys.excepthook(type, value, tb)
+    if isinstance(value, str):
+        # Cython can raise errors where the value is a plain string
+        # e.g., AttributeError, "_semaphore.Semaphore has no attr", <traceback>
+        value = type(value)
+    if not issubclass(type, self.NOT_ERROR):
+        sys.excepthook(type, value, tb)
 
 gevent.hub.Hub.handle_error = handleGreenletError