diff --git a/python/ribasim/ribasim/model.py b/python/ribasim/ribasim/model.py
index 7457b4b45..d46b648b0 100644
--- a/python/ribasim/ribasim/model.py
+++ b/python/ribasim/ribasim/model.py
@@ -307,7 +307,7 @@ def write(self, filepath: str | PathLike[str]) -> Path:
         if self.use_validation:
             self._validate_model()
 
-        if self.edge.df.subnetwork_id.notna().any():
+        if self.edge.df is not None and self.edge.df["subnetwork_id"].notna().any():
             warnings.warn(
                 "Sources for allocation are automatically inferred and no longer have to be specified in the `Edge` table.",
                 DeprecationWarning,