diff --git a/package-lock.json b/package-lock.json
index 434b6090..2413b311 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -2089,7 +2089,8 @@
         "ansi-regex": {
           "version": "2.1.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "aproba": {
           "version": "1.2.0",
@@ -2110,12 +2111,14 @@
         "balanced-match": {
           "version": "1.0.0",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "brace-expansion": {
           "version": "1.1.11",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "balanced-match": "^1.0.0",
             "concat-map": "0.0.1"
@@ -2130,17 +2133,20 @@
         "code-point-at": {
           "version": "1.1.0",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "concat-map": {
           "version": "0.0.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "console-control-strings": {
           "version": "1.1.0",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "core-util-is": {
           "version": "1.0.2",
@@ -2257,7 +2263,8 @@
         "inherits": {
           "version": "2.0.3",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "ini": {
           "version": "1.3.5",
@@ -2269,6 +2276,7 @@
           "version": "1.0.0",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "number-is-nan": "^1.0.0"
           }
@@ -2283,6 +2291,7 @@
           "version": "3.0.4",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "brace-expansion": "^1.1.7"
           }
@@ -2290,12 +2299,14 @@
         "minimist": {
           "version": "0.0.8",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "minipass": {
           "version": "2.3.5",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "safe-buffer": "^5.1.2",
             "yallist": "^3.0.0"
@@ -2314,6 +2325,7 @@
           "version": "0.5.1",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "minimist": "0.0.8"
           }
@@ -2394,7 +2406,8 @@
         "number-is-nan": {
           "version": "1.0.1",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "object-assign": {
           "version": "4.1.1",
@@ -2406,6 +2419,7 @@
           "version": "1.4.0",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "wrappy": "1"
           }
@@ -2491,7 +2505,8 @@
         "safe-buffer": {
           "version": "5.1.2",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "safer-buffer": {
           "version": "2.1.2",
@@ -2527,6 +2542,7 @@
           "version": "1.0.2",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "code-point-at": "^1.0.0",
             "is-fullwidth-code-point": "^1.0.0",
@@ -2546,6 +2562,7 @@
           "version": "3.0.1",
           "bundled": true,
           "dev": true,
+          "optional": true,
           "requires": {
             "ansi-regex": "^2.0.0"
           }
@@ -2589,12 +2606,14 @@
         "wrappy": {
           "version": "1.0.2",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         },
         "yallist": {
           "version": "3.0.3",
           "bundled": true,
-          "dev": true
+          "dev": true,
+          "optional": true
         }
       }
     },
diff --git a/package.json b/package.json
index d8131a2d..1d340d22 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "svelte-preprocess",
-  "version": "2.5.0",
+  "version": "2.5.1",
   "license": "MIT",
   "main": "src/index.js",
   "types": "src/index.d.ts",
diff --git a/src/utils.js b/src/utils.js
index c258f0c6..967dad9a 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -68,15 +68,15 @@ exports.addLanguageAlias = entries =>
   entries.forEach(entry => LANG_DICT.set(...entry))
 
 exports.getLanguage = (attributes, defaultLang) => {
-  let lang
+  let lang = defaultLang
 
-  if (attributes.src) {
+  if (attributes.lang) {
+    lang = attributes.lang
+  } else if (attributes.type) {
+    lang = attributes.type.replace(/^(text|application)\/(.*)$/, '$2')
+  } else if (attributes.src) {
     lang = attributes.src.match(/\.([^/.]+)$/)
     lang = lang ? lang[1] : defaultLang
-  } else {
-    lang = attributes.type
-      ? attributes.type.replace(/^(text|application)\/(.*)$/, '$2')
-      : attributes.lang || defaultLang
   }
 
   return {
diff --git a/test/fixtures/template.custom b/test/fixtures/template.custom
new file mode 100644
index 00000000..19102815
--- /dev/null
+++ b/test/fixtures/template.custom
@@ -0,0 +1 @@
+foo
\ No newline at end of file
diff --git a/test/index.test.js b/test/index.test.js
index 4533aff6..1afc7fbb 100644
--- a/test/index.test.js
+++ b/test/index.test.js
@@ -263,10 +263,11 @@ describe('detect - mimetype', () => {
     { type: 'application/ld+json', parser: 'ld+json' },
     { type: 'text/some-other', parser: 'some-other' },
     { lang: 'stylus', parser: 'stylus' },
+    { src: '../foo.custom', lang: 'customLanguage', parser: 'customLanguage' },
   ]
-  MIMETYPES.forEach(({ type, lang, parser }) => {
-    it(`should detect ${type || lang} as ${parser}`, async () => {
-      expect(getLanguage({ type, lang }, 'javascript')).toEqual({
+  MIMETYPES.forEach(({ type, lang, src, parser }) => {
+    it(`should detect '${src || type || lang}' as '${parser}'`, async () => {
+      expect(getLanguage({ type, lang, src }, 'javascript')).toEqual({
         lang: parser,
         alias: parser,
       })
@@ -330,17 +331,19 @@ describe('external files', () => {
 
 describe('options', () => {
   it('should accept custom method for a transformer', async () => {
-    const input = `<template src="./fixtures/template.pug"></template>`
+    const input = `<template lang="customTransformer">${getFixtureContent(
+      'template.custom',
+    )}</template>`
     const opts = getPreprocess({
-      pug: (content, filename) => {
-        const code = require('pug').render(content, opts)
-        return {
-          code,
-        }
+      transformers: {
+        customTransformer({ content, filename }) {
+          content = content.replace('foo', 'bar')
+          return { code: content, map: null }
+        },
       },
     })
     const preprocessed = (await preprocess(input, opts)).trim()
-    expect(preprocessed).toBe(parsedMarkup)
+    expect(preprocessed).toBe('bar')
   })
 
   it('should accept an options object as transformer value', async () => {