diff --git a/src/farm/index.ts b/src/farm/index.ts
index f7e7855f..f3c06e6c 100644
--- a/src/farm/index.ts
+++ b/src/farm/index.ts
@@ -28,8 +28,8 @@ import {
   customParseQueryString,
   decodeStr,
   encodeStr,
+  formatTransformModuleType,
   getContentValue,
-  guessIdLoader,
   isObject,
   isStartsWithSlash,
   isString,
@@ -161,7 +161,7 @@ export function toFarmPlugin(plugin: UnpluginOptions, options?: Record<string, a
 
         const id = appendQuery(resolvedPath, params.query)
 
-        const loader = guessIdLoader(resolvedPath)
+        const loader = formatTransformModuleType(id)
 
         const shouldLoadInclude
           = plugin.loadInclude?.(id)
@@ -198,7 +198,7 @@ export function toFarmPlugin(plugin: UnpluginOptions, options?: Record<string, a
 
         const id = appendQuery(resolvedPath, params.query)
 
-        const loader = params.moduleType ?? guessIdLoader(params.resolvedPath)
+        const loader = formatTransformModuleType(id)
 
         const shouldTransformInclude
           = plugin.transformInclude?.(id)
@@ -216,7 +216,9 @@ export function toFarmPlugin(plugin: UnpluginOptions, options?: Record<string, a
           const transformFarmResult: PluginTransformHookResult = {
             content: getContentValue(resource),
             moduleType: loader,
-            sourceMap: JSON.stringify(resource.map),
+            sourceMap: typeof resource.map === 'object' && resource.map !== null
+              ? JSON.stringify(resource.map)
+              : undefined,
           }
 
           return transformFarmResult
diff --git a/src/farm/utils.ts b/src/farm/utils.ts
index 88d869ae..00c896c7 100644
--- a/src/farm/utils.ts
+++ b/src/farm/utils.ts
@@ -213,3 +213,60 @@ export function stringifyQuery(query: [string, string][]): string {
 export interface JsPluginExtended extends JsPlugin {
   [key: string]: any
 }
+
+export const CSS_LANGS_RES: [RegExp, string][] = [
+  [/\.(less)(?:$|\?)/, 'less'],
+  [/\.(scss|sass)(?:$|\?)/, 'sass'],
+  [/\.(styl|stylus)(?:$|\?)/, 'stylus'],
+  [/\.(css)(?:$|\?)/, 'css'],
+]
+
+export const JS_LANGS_RES: [RegExp, string][] = [
+  [/\.(js|mjs|cjs)(?:$|\?)/, 'js'],
+  // jsx
+  [/\.(jsx)(?:$|\?)/, 'jsx'],
+  // ts
+  [/\.(ts|cts|mts)(?:$|\?)/, 'ts'],
+  // tsx
+  [/\.(tsx)(?:$|\?)/, 'tsx'],
+]
+
+export function getCssModuleType(id: string): string | null {
+  for (const [reg, lang] of CSS_LANGS_RES) {
+    if (reg.test(id)) {
+      return lang
+    }
+  }
+
+  return null
+}
+
+export function getJsModuleType(id: string): string | null {
+  for (const [reg, lang] of JS_LANGS_RES) {
+    if (reg.test(id)) {
+      return lang
+    }
+  }
+
+  return null
+}
+
+export function formatLoadModuleType(id: string): string {
+  const cssModuleType = getCssModuleType(id)
+
+  if (cssModuleType) {
+    return cssModuleType
+  }
+
+  const jsModuleType = getJsModuleType(id)
+
+  if (jsModuleType) {
+    return jsModuleType
+  }
+
+  return 'js'
+}
+
+export function formatTransformModuleType(id: string): string {
+  return formatLoadModuleType(id)
+}