diff --git a/.babelrc b/.babelrc
index 7790c037..ba54da8f 100644
--- a/.babelrc
+++ b/.babelrc
@@ -4,7 +4,7 @@
       "loose": true,
       "targets": {
         "browsers": ["last 2 versions", "safari >= 7", "ie 9"],
-        "node": "4"
+        "node": "6"
       }
     }]
   ],
diff --git a/.travis.yml b/.travis.yml
index 1000b75c..4c3d5e3b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,9 +1,9 @@
 language: node_js
 sudo: false
 node_js:
+  - "9"
   - "8"
   - "6"
-  - "4"
 install:
   - npm install
   - npm install codecov
diff --git a/appveyor.yml b/appveyor.yml
index b44b1867..341eec16 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -5,9 +5,9 @@ init:
 # Test against these versions of Node.js.
 environment:
   matrix:
+    - nodejs_version: "9"
     - nodejs_version: "8"
     - nodejs_version: "6"
-    - nodejs_version: "4"
 
 # Install scripts. (runs after repo cloning)
 install: