diff --git a/source-map-uploader-plugin.js b/source-map-uploader-plugin.js
index 70723a3..0a6415a 100644
--- a/source-map-uploader-plugin.js
+++ b/source-map-uploader-plugin.js
@@ -3,6 +3,7 @@
 const upload = require('bugsnag-sourcemaps').upload
 const resolve = require('url').resolve
 const parallel = require('run-parallel-limit')
+const extname = require('path').extname
 
 const LOG_PREFIX = `[BugsnagSourceMapUploaderPlugin]`
 const PUBLIC_PATH_ERR =
@@ -17,6 +18,7 @@ class BugsnagSourceMapUploaderPlugin {
     this.appVersion = options.appVersion
     this.overwrite = options.overwrite
     this.endpoint = options.endpoint
+    this.extensions = options.extensions || [ '.js' ]
     this.validate()
   }
 
@@ -59,6 +61,13 @@ class BugsnagSourceMapUploaderPlugin {
             return null
           }
 
+          // only include this file if its extension is in the list of desirable ones.
+          // we use the extension from the file on disk because the name in the chunk
+          // can have suffixes such as: main.js?23764
+          if (!this.extensions.includes(extname(compilation.assets[source].existsAt))) {
+            return null
+          }
+
           return {
             source: compilation.assets[source].existsAt,
             map: compilation.assets[map].existsAt,
diff --git a/test/fixtures/e/webpack.config.js b/test/fixtures/e/webpack.config.js
index 5165fbe..0a26069 100644
--- a/test/fixtures/e/webpack.config.js
+++ b/test/fixtures/e/webpack.config.js
@@ -8,7 +8,8 @@ module.exports = {
     new MiniCssExtractPlugin(),
     new BugsnagSourceMapUploaderPlugin({
       apiKey: 'YOUR_API_KEY',
-      endpoint: `http://localhost:${process.env.PORT}`
+      endpoint: `http://localhost:${process.env.PORT}`,
+      extensions: process.env.EXTENSIONS ? process.env.EXTENSIONS.split(',') : undefined
     })
   ],
   output: {
diff --git a/test/source-map-uploader-plugin.test.js b/test/source-map-uploader-plugin.test.js
index 79b4cc5..4ff18bd 100644
--- a/test/source-map-uploader-plugin.test.js
+++ b/test/source-map-uploader-plugin.test.js
@@ -120,8 +120,52 @@ test('it sends upon successful build (example project #2)', t => {
 })
 
 if (process.env.WEBPACK_VERSION !== '3') {
-  test('it works when plugins cause a chunk to have multiple source maps', t => {
-    t.plan(7)
+  test('it ignores source maps for css files by default', t => {
+    t.plan(3)
+    const requests = []
+    const end = err => {
+      clearTimeout(timeout)
+      server.close()
+      if (err) return t.fail(err.message)
+      t.end()
+    }
+
+    // prevent test hanging forever
+    const timeout = setTimeout(end, 10000)
+
+    const done = () => {
+      t.equal(requests[0].minifiedUrl, '*/dist/main.js')
+      t.equal(requests[0].parts[0].filename, 'main.js.map')
+      t.equal(requests[0].parts[1].filename, 'main.js')
+      end()
+    }
+
+    const server = http.createServer((req, res) => {
+      parseFormdata(req, function (err, data) {
+        if (err) {
+          res.end('ERR')
+          return end(err)
+        }
+        requests.push({
+          apiKey: data.fields.apiKey,
+          minifiedUrl: data.fields.minifiedUrl,
+          parts: data.parts.map(p => ({ name: p.name, filename: p.filename }))
+        })
+        res.end('OK')
+        done()
+      })
+    })
+    server.listen()
+    exec(`${__dirname}/../node_modules/.bin/webpack`, {
+      env: Object.assign({}, process.env, { PORT: server.address().port }),
+      cwd: `${__dirname}/fixtures/e`
+    }, (err) => {
+      if (err) end(err)
+    })
+  })
+
+  test('it uploads css map files if you really want', t => {
+    t.plan(6)
     const requests = []
     const end = err => {
       clearTimeout(timeout)
@@ -134,12 +178,11 @@ if (process.env.WEBPACK_VERSION !== '3') {
     const timeout = setTimeout(end, 10000)
 
     const done = () => {
-      t.equal(requests.length, 2)
       requests.sort((a, b) => a.minifiedUrl < b.minifiedUrl ? -1 : 1)
       t.equal(requests[0].minifiedUrl, '*/dist/main.css')
-      t.equal(requests[1].minifiedUrl, '*/dist/main.js')
       t.equal(requests[0].parts[0].filename, 'main.css.map')
       t.equal(requests[0].parts[1].filename, 'main.css')
+      t.equal(requests[1].minifiedUrl, '*/dist/main.js')
       t.equal(requests[1].parts[0].filename, 'main.js.map')
       t.equal(requests[1].parts[1].filename, 'main.js')
       end()
@@ -157,12 +200,13 @@ if (process.env.WEBPACK_VERSION !== '3') {
           parts: data.parts.map(p => ({ name: p.name, filename: p.filename }))
         })
         res.end('OK')
-        if (requests.length === 2) done()
+        if (requests.length < 2) return
+        done()
       })
     })
     server.listen()
     exec(`${__dirname}/../node_modules/.bin/webpack`, {
-      env: Object.assign({}, process.env, { PORT: server.address().port }),
+      env: Object.assign({}, process.env, { PORT: server.address().port, EXTENSIONS: '.js,.css' }),
       cwd: `${__dirname}/fixtures/e`
     }, (err) => {
       if (err) end(err)