diff --git a/extensions/functions_string.yaml b/extensions/functions_string.yaml
index 3599ae589..ad9fd4a32 100644
--- a/extensions/functions_string.yaml
+++ b/extensions/functions_string.yaml
@@ -657,10 +657,10 @@ aggregate_functions:
     description: Concatenates a column of string values with a separator.
     impls:
       - args:
-          - value: "varchar<L1>"
+          - value: "string"
             name: "input"
             description: "Column of string values."
-          - value: "varchar<L2>"
+          - value: "string"
             name: "separator"
             description: "Separator for concatenated strings"
-        return: "varchar<L1 + L2>"
\ No newline at end of file
+        return: "string"
\ No newline at end of file