diff --git a/src/kiara_plugin/topic_modelling/modules/corpus_preparation.py b/src/kiara_plugin/topic_modelling/modules/corpus_preparation.py
index 2a55c61..f6de783 100644
--- a/src/kiara_plugin/topic_modelling/modules/corpus_preparation.py
+++ b/src/kiara_plugin/topic_modelling/modules/corpus_preparation.py
@@ -130,6 +130,9 @@ def create_inputs_schema(self):
         return {
              "periodicity": {
                 "type": "string",
+                "type_config": {
+                "allowed_strings": ["day", "month", "year"]
+            },
                 "doc": "The desired data periodicity to aggregate the data. Values can be either 'day','month' or 'year'."
             },
             "date_col_name": {