diff --git a/b_asic/signal_flow_graph.py b/b_asic/signal_flow_graph.py
index 5e01feaf8b9888372f63355393059d4abf683971..6529dfd7d355f062c18ae16f2307587ec5e4cd80 100644
--- a/b_asic/signal_flow_graph.py
+++ b/b_asic/signal_flow_graph.py
@@ -284,7 +284,7 @@ class SFG(AbstractOperation):
     def split(self) -> Iterable[Operation]:
         return self.operations
     
-    def to_sfg(self) -> SFG:
+    def to_sfg(self) -> 'SFG':
         return self
 
     def inputs_required_for_output(self, output_index: int) -> Iterable[int]: