diff --git a/src/azure_data_factory_testing_framework/functions/expression_evaluator.py b/src/azure_data_factory_testing_framework/functions/expression_evaluator.py
index 4658be35..ee9e052c 100644
--- a/src/azure_data_factory_testing_framework/functions/expression_evaluator.py
+++ b/src/azure_data_factory_testing_framework/functions/expression_evaluator.py
@@ -80,10 +80,8 @@ def __init__(self) -> None:
         base_grammar = """
             ?start: ("@" expression_start) | (["@@"] literal_start)
             
-            // shared rules
-            ARRAY_INDEX: "[" /[0-9]+/ "]"
-
             // shared custom basic data type rules:
+            ARRAY_INDEX: "[" /[0-9]+/ "]"
             NULL: "null"
             BOOLEAN: "true" | "false"
             SINGLE_QUOTED_STRING: "'" /([^']|'')*/ "'"