diff --git a/pymathics/graph/format.py b/pymathics/graph/format.py
index 24c0899..edbe44e 100644
--- a/pymathics/graph/format.py
+++ b/pymathics/graph/format.py
@@ -35,7 +35,7 @@ def format_graph(G, **options) -> str:
 
     global node_size
     global cached_pair
-
+    pyplot.close()
     pyplot.switch_backend("AGG")
     cached_pair = None