diff --git a/src/gfn/preprocessors.py b/src/gfn/preprocessors.py
index 599d794a..f37e87f9 100644
--- a/src/gfn/preprocessors.py
+++ b/src/gfn/preprocessors.py
@@ -77,7 +77,7 @@ def preprocess(self, states) -> torch.Tensor:
 
 class GraphPreprocessor(Preprocessor):
     def __init__(self) -> None:
-        super().__init__(-1)
+        super().__init__(-1)  # TODO: review output_dim API
 
     def preprocess(self, states: GraphStates) -> TensorDict:
         return states.tensor