diff --git a/src/simudator/gui/processor_handler.py b/src/simudator/gui/processor_handler.py
index 91612fd9a6e5af44e70f145e0745729c632d44a7..9a9e9b3321f5fcb82c00be6bd77dbd362751ab53 100644
--- a/src/simudator/gui/processor_handler.py
+++ b/src/simudator/gui/processor_handler.py
@@ -310,7 +310,7 @@ class ProcessorHandler(QObject):
             self._processor.undo_asm_instruction(instructions)
             self._signal_processor_changed()
         except (ValueError, IndexError):
-            self._error_msg_box("Unable to undo the instruction.")
+            self._error_msg_box.showMessage("Unable to undo the instruction.")
 
     @Slot()
     def toggle_value_update_on_run(self):