diff --git a/cime_config/MOM_RPS/FType_MOM_params.py b/cime_config/MOM_RPS/FType_MOM_params.py
index 79da6ad..fca84e6 100644
--- a/cime_config/MOM_RPS/FType_MOM_params.py
+++ b/cime_config/MOM_RPS/FType_MOM_params.py
@@ -83,7 +83,7 @@ def _read_MOM_input(input_path):
                                         "ERROR: "
                                         + varname
                                         + " listed more than once in "
-                                        + input_path
+                                        + str(input_path)
                                     )
 
                                 # enter the parameter in the dictionary: