diff --git a/python/ngen_cal/src/ngen/cal/calibration_set.py b/python/ngen_cal/src/ngen/cal/calibration_set.py
index f2a8a76e..c750a88f 100644
--- a/python/ngen_cal/src/ngen/cal/calibration_set.py
+++ b/python/ngen_cal/src/ngen/cal/calibration_set.py
@@ -62,7 +62,10 @@ def output(self) -> 'DataFrame':
         """
         # TODO should contributing_catchments be singular??? assuming it is for now...
         # Call output hooks, take first non-none result provided from hooks (called in LIFO order of registration)
-        df = self._hooks.ngen_cal_model_output(id=self._eval_nexus.contributing_catchments[0].replace('cat', 'wb'))
+        cat_id = self._eval_nexus.contributing_catchments[0].id
+        assert cat_id.startswith("cat"), f"expected catchment id to start with 'cat': {cat_id}"
+        cat_id = cat_id.replace("cat", "wb")
+        df = self._hooks.ngen_cal_model_output(id=cat_id)
         if df is None:
             # list of results is empty
             print("No suitable output found from output hooks...")
@@ -144,4 +147,4 @@ def restart(self):
         except FileNotFoundError:
             return 0
         #Reload the evaluation information
-        return Evaluatable.restart(self)
\ No newline at end of file
+        return Evaluatable.restart(self)