diff --git a/b_asic/signal_flow_graph.py b/b_asic/signal_flow_graph.py
index 950926f48212e825125a0122a272def557499b69..e8e7af01ab93fdba948d9ff7ec19078b3b71dee6 100644
--- a/b_asic/signal_flow_graph.py
+++ b/b_asic/signal_flow_graph.py
@@ -156,7 +156,7 @@ class SFG(AbstractOperation):
                 if signal.source.operation not in self._original_components_to_new:
                     self._add_operation_connected_tree_copy(signal.source.operation)
     
-    def __str__(self):
+    def __str__(self) -> str:
         """Get a string representation of this SFG."""
         output_string = ""
         for component in self._components_ordered: