diff --git a/package.json b/package.json
index 2d49ebd5..f2d61dae 100644
--- a/package.json
+++ b/package.json
@@ -13,8 +13,8 @@
     "dev": "babel -w src -d lib",
     "lint": "eslint .",
     "fix": "eslint . --fix",
-    "cov": "nyc npm run test",
-    "ci": "nyc npm run test && nyc report --reporter=json && codecov -f coverage/coverage-final.json",
+    "cov": "BABEL_ENV=test nyc npm run test",
+    "ci": "npm run cov && nyc report --reporter=json && codecov -f coverage/coverage-final.json",
     "changelog": "git log `git describe --tags --abbrev=0`..HEAD --pretty=format:' * %s (%an)' | grep -v 'Merge pull request'",
     "test": "npm run build && mocha ./test --compilers js:babel-register -t 10000"
   },
@@ -55,6 +55,7 @@
     "babel-eslint": "^7.1.1",
     "babel-helper-fixtures": "^6.22.0",
     "babel-helper-plugin-test-runner": "^6.18.0",
+    "babel-plugin-istanbul": "^4.0.0",
     "babel-plugin-transform-flow-strip-types": "^6.8.0",
     "babel-preset-es2015": "^6.14.0",
     "babel-register": "^6.14.0",
@@ -81,6 +82,15 @@
     ],
     "plugins": [
       "transform-flow-strip-types"
-    ]
+    ],
+    "env": {
+      "test": {
+        "plugins": ["istanbul"]
+      }
+    }
+  },
+  "nyc": {
+    "all": true,
+    "include": ["src/*.js"]
   }
 }
diff --git a/yarn.lock b/yarn.lock
index b690c65b..ee2ab928 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -425,6 +425,14 @@ babel-plugin-check-es2015-constants@^6.3.13:
   dependencies:
     babel-runtime "^6.0.0"
 
+babel-plugin-istanbul@^4.0.0:
+  version "4.0.0"
+  resolved "https://registry.yarnpkg.com/babel-plugin-istanbul/-/babel-plugin-istanbul-4.0.0.tgz#36bde8fbef4837e5ff0366531a2beabd7b1ffa10"
+  dependencies:
+    find-up "^2.1.0"
+    istanbul-lib-instrument "^1.4.2"
+    test-exclude "^4.0.0"
+
 babel-plugin-syntax-async-functions@^6.8.0:
   version "6.13.0"
   resolved "https://registry.yarnpkg.com/babel-plugin-syntax-async-functions/-/babel-plugin-syntax-async-functions-6.13.0.tgz#cad9cad1191b5ad634bf30ae0872391e0647be95"
@@ -1728,6 +1736,12 @@ find-up@^1.0.0, find-up@^1.1.2:
     path-exists "^2.0.0"
     pinkie-promise "^2.0.0"
 
+find-up@^2.1.0:
+  version "2.1.0"
+  resolved "https://registry.yarnpkg.com/find-up/-/find-up-2.1.0.tgz#45d1b7e506c717ddd482775a2b77920a3c0c57a7"
+  dependencies:
+    locate-path "^2.0.0"
+
 flat-cache@^1.2.1:
   version "1.2.2"
   resolved "https://registry.yarnpkg.com/flat-cache/-/flat-cache-1.2.2.tgz#fa86714e72c21db88601761ecf2f555d1abc6b96"
@@ -1870,7 +1884,7 @@ glob@5.0.x, glob@^5.0.15, glob@^5.0.5:
     once "^1.3.0"
     path-is-absolute "^1.0.0"
 
-glob@7.0.5, glob@^7.0.0, glob@^7.0.3, glob@^7.0.5:
+glob@7.0.5, glob@^7.0.3:
   version "7.0.5"
   resolved "https://registry.yarnpkg.com/glob/-/glob-7.0.5.tgz#b4202a69099bbb4d292a7c1b95b6682b67ebdc95"
   dependencies:
@@ -1881,7 +1895,7 @@ glob@7.0.5, glob@^7.0.0, glob@^7.0.3, glob@^7.0.5:
     once "^1.3.0"
     path-is-absolute "^1.0.0"
 
-glob@^7.0.6, glob@^7.1.1:
+glob@^7.0.0, glob@^7.0.5, glob@^7.0.6, glob@^7.1.1:
   version "7.1.1"
   resolved "https://registry.yarnpkg.com/glob/-/glob-7.1.1.tgz#805211df04faaf1c63a3600306cdf5ade50b2ec8"
   dependencies:
@@ -2419,6 +2433,13 @@ load-json-file@^1.0.0:
     pinkie-promise "^2.0.0"
     strip-bom "^2.0.0"
 
+locate-path@^2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/locate-path/-/locate-path-2.0.0.tgz#2b568b265eec944c6d9c0de9c3dbbbca0354cd8e"
+  dependencies:
+    p-locate "^2.0.0"
+    path-exists "^3.0.0"
+
 lodash._baseassign@^3.0.0:
   version "3.2.0"
   resolved "https://registry.yarnpkg.com/lodash._baseassign/-/lodash._baseassign-3.2.0.tgz#8c38a099500f215ad09e59f1722fd0c52bfe0a4e"
@@ -2791,6 +2812,16 @@ output-file-sync@^1.1.0:
     mkdirp "^0.5.1"
     object-assign "^4.1.0"
 
+p-limit@^1.1.0:
+  version "1.1.0"
+  resolved "https://registry.yarnpkg.com/p-limit/-/p-limit-1.1.0.tgz#b07ff2d9a5d88bec806035895a2bab66a27988bc"
+
+p-locate@^2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/p-locate/-/p-locate-2.0.0.tgz#20a0103b222a70c8fd39cc2e580680f3dde5ec43"
+  dependencies:
+    p-limit "^1.1.0"
+
 parse-glob@^3.0.4:
   version "3.0.4"
   resolved "https://registry.yarnpkg.com/parse-glob/-/parse-glob-3.0.4.tgz#b2c376cfb11f35513badd173ef0bb6e3a388391c"
@@ -2816,6 +2847,10 @@ path-exists@^2.0.0:
   dependencies:
     pinkie-promise "^2.0.0"
 
+path-exists@^3.0.0:
+  version "3.0.0"
+  resolved "https://registry.yarnpkg.com/path-exists/-/path-exists-3.0.0.tgz#ce0ebeaa5f78cb18925ea7d810d7b59b010fd515"
+
 path-is-absolute@^1.0.0:
   version "1.0.1"
   resolved "https://registry.yarnpkg.com/path-is-absolute/-/path-is-absolute-1.0.1.tgz#174b9268735534ffbc7ace6bf53a5a9e1b5c5f5f"
@@ -3454,6 +3489,16 @@ test-exclude@^3.3.0:
     read-pkg-up "^1.0.1"
     require-main-filename "^1.0.1"
 
+test-exclude@^4.0.0:
+  version "4.0.0"
+  resolved "https://registry.yarnpkg.com/test-exclude/-/test-exclude-4.0.0.tgz#0ddc0100b8ae7e88b34eb4fd98a907e961991900"
+  dependencies:
+    arrify "^1.0.1"
+    micromatch "^2.3.11"
+    object-assign "^4.1.0"
+    read-pkg-up "^1.0.1"
+    require-main-filename "^1.0.1"
+
 text-table@~0.2.0:
   version "0.2.0"
   resolved "https://registry.yarnpkg.com/text-table/-/text-table-0.2.0.tgz#7f5ee823ae805207c00af2df4a84ec3fcfa570b4"