diff --git a/package.json b/package.json
index 54cbb32..280a339 100644
--- a/package.json
+++ b/package.json
@@ -26,7 +26,7 @@
   },
   "devDependencies": {
     "blanket": "~1.2.3",
-    "chai": "^2.3.0",
+    "chai": "^4.3.4",
     "chai-as-promised": "^7.1.1",
     "coffee-script": "^1.12.7",
     "mocha": "^2.2.5",
diff --git a/yarn.lock b/yarn.lock
index 70e90da..a44c30f 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -10,9 +10,10 @@ acorn@^1.0.3:
   version "1.2.2"
   resolved "https://registry.npmjs.org/acorn/-/acorn-1.2.2.tgz#c8ce27de0acc76d896d2b1fad3df588d9e82f014"
 
-assertion-error@1.0.0:
-  version "1.0.0"
-  resolved "https://registry.npmjs.org/assertion-error/-/assertion-error-1.0.0.tgz#c7f85438fdd466bc7ca16ab90c81513797a5d23b"
+assertion-error@^1.1.0:
+  version "1.1.0"
+  resolved "https://registry.npmjs.org/assertion-error/-/assertion-error-1.1.0.tgz#e60b6b0e8f301bd97e5375215bda406c85118c0b"
+  integrity sha512-jgsaNduz+ndvGyFt3uSuWqvy4lCnIJiovtouQN5JZHOKCS2QuhEdbcQHFhVksz2N2U9hXJo8odG7ETyWlEeuDw==
 
 async@2.1.4:
   version "2.1.4"
@@ -53,13 +54,17 @@ chai-as-promised@^7.1.1:
   dependencies:
     check-error "^1.0.2"
 
-chai@^2.3.0:
-  version "2.3.0"
-  resolved "https://registry.npmjs.org/chai/-/chai-2.3.0.tgz#8a2f6a34748da801090fd73287b2aa739a4e909a"
-  integrity sha1-ii9qNHSNqAEJD9cyh7Kqc5pOkJo=
+chai@^4.3.4:
+  version "4.3.4"
+  resolved "https://registry.npmjs.org/chai/-/chai-4.3.4.tgz#b55e655b31e1eac7099be4c08c21964fce2e6c49"
+  integrity sha512-yS5H68VYOCtN1cjfwumDSuzn/9c+yza4f3reKXlE5rUg7SFcCEy90gJvydNgOYtblyf4Zi6jIWRnXOgErta0KA==
   dependencies:
-    assertion-error "1.0.0"
-    deep-eql "0.1.3"
+    assertion-error "^1.1.0"
+    check-error "^1.0.2"
+    deep-eql "^3.0.1"
+    get-func-name "^2.0.0"
+    pathval "^1.1.1"
+    type-detect "^4.0.5"
 
 chance@^1.1.7:
   version "1.1.7"
@@ -98,11 +103,12 @@ debug@^4.3.1:
   dependencies:
     ms "2.1.2"
 
-deep-eql@0.1.3:
-  version "0.1.3"
-  resolved "https://registry.npmjs.org/deep-eql/-/deep-eql-0.1.3.tgz#ef558acab8de25206cd713906d74e56930eb69f2"
+deep-eql@^3.0.1:
+  version "3.0.1"
+  resolved "https://registry.npmjs.org/deep-eql/-/deep-eql-3.0.1.tgz#dfc9404400ad1c8fe023e7da1df1c147c4b444df"
+  integrity sha512-+QeIQyN5ZuO+3Uk5DYh6/1eKO0m0YmJFGNmFHGACpf1ClL1nmlV/p4gNgbl2pJGxgXb4faqo6UE+M5ACEMyVcw==
   dependencies:
-    type-detect "0.1.1"
+    type-detect "^4.0.0"
 
 diff@1.4.0:
   version "1.4.0"
@@ -137,6 +143,11 @@ foreach@^2.0.5:
   version "2.0.5"
   resolved "https://registry.npmjs.org/foreach/-/foreach-2.0.5.tgz#0bee005018aeb260d0a3af3ae658dd0136ec1b99"
 
+get-func-name@^2.0.0:
+  version "2.0.0"
+  resolved "https://registry.npmjs.org/get-func-name/-/get-func-name-2.0.0.tgz#ead774abee72e20409433a066366023dd6887a41"
+  integrity sha1-6td0q+5y4gQJQzoGY2YCPdaIekE=
+
 glob@3.2.11:
   version "3.2.11"
   resolved "https://registry.npmjs.org/glob/-/glob-3.2.11.tgz#4a973f635b9190f715d10987d5c00fd2815ebe3d"
@@ -298,6 +309,11 @@ object-keys@^1.0.6:
   version "1.0.11"
   resolved "https://registry.npmjs.org/object-keys/-/object-keys-1.0.11.tgz#c54601778ad560f1142ce0e01bcca8b56d13426d"
 
+pathval@^1.1.1:
+  version "1.1.1"
+  resolved "https://registry.npmjs.org/pathval/-/pathval-1.1.1.tgz#8534e77a77ce7ac5a2512ea21e0fdb8fcf6c3d8d"
+  integrity sha512-Dp6zGqpTdETdR63lehJYPeIOqpiNBNtc7BpWSLrOje7UaIsE5aY92r/AunQA7rsXvet3lrJ3JnZX29UPTKXyKQ==
+
 process-nextick-args@~1.0.6:
   version "1.0.7"
   resolved "https://registry.npmjs.org/process-nextick-args/-/process-nextick-args-1.0.7.tgz#150e20b756590ad3f91093f25a4f2ad8bff30ba3"
@@ -361,9 +377,10 @@ tv4@^1.2.7:
   version "1.3.0"
   resolved "https://registry.npmjs.org/tv4/-/tv4-1.3.0.tgz#d020c846fadd50c855abb25ebaecc68fc10f7963"
 
-type-detect@0.1.1:
-  version "0.1.1"
-  resolved "https://registry.npmjs.org/type-detect/-/type-detect-0.1.1.tgz#0ba5ec2a885640e470ea4e8505971900dac58822"
+type-detect@^4.0.0, type-detect@^4.0.5:
+  version "4.0.8"
+  resolved "https://registry.npmjs.org/type-detect/-/type-detect-4.0.8.tgz#7646fb5f18871cfbb7749e69bd39a6388eb7450c"
+  integrity sha512-0fr/mIH1dlO+x7TlcMy+bIDqKPsw/70tVyeHW787goQjhmqaZe10uwLujubK9q9Lg6Fiho1KUKDYz0Z7k7g5/g==
 
 util-deprecate@~1.0.1:
   version "1.0.2"