diff --git a/.travis.yml b/.travis.yml
index 2c1aee12..7719cd1d 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -12,6 +12,7 @@ before_script:
   - greenkeeper-lockfile-update
 script:
   - npm run lint
+  - npm test
 after_script: greenkeeper-lockfile-upload
 notifications:
   email: false
diff --git a/README.md b/README.md
index 8ef592e6..1d224d17 100644
--- a/README.md
+++ b/README.md
@@ -50,6 +50,8 @@ npx bundlesize
 #### 1) Add the path and maxSize in your `package.json`.
 By default the gzipped size is tested. You can use the `compression` option to change this. (`gzip`, `brotli`, or `none`).
 
+To use the `brotli` compression option, you must install the peer dependency: `npm install --save brotli-size`
+
 ```json
 {
   "name": "your cool library",
diff --git a/package.json b/package.json
index ecec9008..03ec0f92 100644
--- a/package.json
+++ b/package.json
@@ -39,7 +39,6 @@
   "license": "MIT",
   "dependencies": {
     "axios": "^0.17.0",
-    "brotli-size": "0.0.1",
     "bytes": "^3.0.0",
     "ci-env": "^1.4.0",
     "commander": "^2.11.0",
diff --git a/src/compressed-size.js b/src/compressed-size.js
index e7846924..e676a290 100644
--- a/src/compressed-size.js
+++ b/src/compressed-size.js
@@ -1,5 +1,5 @@
 const gzip = require('gzip-size')
-const brotli = require('brotli-size')
+let brotli
 
 const getCompressedSize = (data, compression = 'gzip') => {
   let size
@@ -8,6 +8,12 @@ const getCompressedSize = (data, compression = 'gzip') => {
       size = gzip.sync(data)
       break
     case 'brotli':
+      try {
+        brotli = require('brotli-size')
+      } catch (e) {
+        throw new Error(`Missing optional dependency. Install it with:
+          npm install --save brotli-size`)
+      }
       size = brotli.sync(data)
       break
     case 'none':