diff --git a/pkg/agent/loop_test.go b/pkg/agent/loop_test.go
index 976d25c4b..1a4a44edf 100644
--- a/pkg/agent/loop_test.go
+++ b/pkg/agent/loop_test.go
@@ -636,8 +636,9 @@ func (m *mockCustomTool) Description() string {
 
 func (m *mockCustomTool) Parameters() map[string]any {
 	return map[string]any{
-		"type":       "object",
-		"properties": map[string]any{},
+		"type":                 "object",
+		"properties":           map[string]any{},
+		"additionalProperties": true,
 	}
 }