diff --git a/src/blenderbim/blenderbim/bim/module/system/operator.py b/src/blenderbim/blenderbim/bim/module/system/operator.py
index f421f77625..33db86f096 100644
--- a/src/blenderbim/blenderbim/bim/module/system/operator.py
+++ b/src/blenderbim/blenderbim/bim/module/system/operator.py
@@ -201,6 +201,11 @@ class SetFlowDirection(bpy.types.Operator, Operator):
     direction: bpy.props.StringProperty()
 
     def _execute(self, context):
+        port = tool.Ifc.get_entity(context.active_object)
+        second_port = tool.System.get_connected_port(port)
+        if not second_port:
+            self.report({"ERROR"}, "To set flow direction port has to be connected to another one.")
+            return
         core.set_flow_direction(
             tool.Ifc, tool.System, port=tool.Ifc.get_entity(context.active_object), direction=self.direction
         )