diff --git a/provider/openaiprovider/chat.go b/provider/openaiprovider/chat.go
index 5195109c..25949273 100644
--- a/provider/openaiprovider/chat.go
+++ b/provider/openaiprovider/chat.go
@@ -308,21 +308,10 @@ func buildCompletionParams(model string, messages []*message.Message, opts []age
 			}
 		case tool.FuncTool:
 			name, description := tl.Name(), tl.Description()
-			var funcParams map[string]any
-			switch schema := tl.Schema().(type) {
-			case map[string]any:
-				funcParams = schema
-			default:
-				if schema == nil {
-					break
-				}
-				data, err := json.Marshal(schema)
-				if err == nil {
-					err = json.Unmarshal(data, &funcParams)
-				}
-				if err != nil {
-					return openai.ChatCompletionNewParams{}, fmt.Errorf("failed to convert function tool schema to JSON format: %w", err)
-				}
+			schema := tl.Schema()
+			funcParams, err := schemaToMap(schema)
+			if err != nil {
+				return openai.ChatCompletionNewParams{}, fmt.Errorf("failed to convert function tool schema to JSON format: %w", err)
 			}
 			params.Tools = append(params.Tools, openai.ChatCompletionToolUnionParam{
 				OfFunction: &openai.ChatCompletionFunctionToolParam{
diff --git a/provider/openaiprovider/responses.go b/provider/openaiprovider/responses.go
index 371e0801..1b712031 100644
--- a/provider/openaiprovider/responses.go
+++ b/provider/openaiprovider/responses.go
@@ -327,21 +327,10 @@ func responsesBuildCompletionParams(config AgentConfig, messages []*message.Mess
 		switch tl := tl.(type) {
 		case tool.FuncTool:
 			name, description := tl.Name(), tl.Description()
-			var funcParams map[string]any
-			switch schema := tl.Schema().(type) {
-			case map[string]any:
-				funcParams = schema
-			default:
-				if schema == nil {
-					break
-				}
-				data, err := json.Marshal(schema)
-				if err == nil {
-					err = json.Unmarshal(data, &funcParams)
-				}
-				if err != nil {
-					return responses.ResponseNewParams{}, fmt.Errorf("failed to convert schema for function tool %q (type %T) to JSON format: %w", name, schema, err)
-				}
+			schema := tl.Schema()
+			funcParams, err := schemaToMap(schema)
+			if err != nil {
+				return responses.ResponseNewParams{}, fmt.Errorf("failed to convert schema for function tool %q (type %T) to JSON format: %w", name, schema, err)
 			}
 			params.Tools = append(params.Tools, responses.ToolUnionParam{
 				OfFunction: &responses.FunctionToolParam{
@@ -771,6 +760,9 @@ func responsesBuildMessageParam(msg *message.Message, resp responses.ResponseInp
 }
 
 func schemaToMap(schema any) (map[string]any, error) {
+	if schema == nil {
+		return nil, nil
+	}
 	if schemaMap, ok := schema.(map[string]any); ok {
 		return schemaMap, nil
 	}