diff --git a/Server/src/services/custom_tool_service.py b/Server/src/services/custom_tool_service.py
index f81b7c70e..36685e3bb 100644
--- a/Server/src/services/custom_tool_service.py
+++ b/Server/src/services/custom_tool_service.py
@@ -433,7 +433,7 @@ def _build_signature(self, definition: ToolDefinitionModel) -> inspect.Signature
             params.append(
                 inspect.Parameter(
                     param.name,
-                    inspect.Parameter.POSITIONAL_OR_KEYWORD,
+                    inspect.Parameter.KEYWORD_ONLY,
                     default=default,
                     annotation=self._map_param_type(param),
                 )