diff --git a/pyzx/graph/multigraph.py b/pyzx/graph/multigraph.py
index f2d2a858..66407ae7 100644
--- a/pyzx/graph/multigraph.py
+++ b/pyzx/graph/multigraph.py
@@ -244,7 +244,7 @@ def remove_edge(self, edge):
 
         if e.is_empty():
             del self.graph[s][t]
-            del self.graph[t][s]
+            if s != t: del self.graph[t][s]
 
         self.nedges -= 1