diff --git a/Gemfile b/Gemfile
index 72c6067..f7cdbc7 100644
--- a/Gemfile
+++ b/Gemfile
@@ -41,7 +41,7 @@ group :test do
   gem "nyan-cat-formatter", require: false
 
   # test coverage
-  gem "simplecov",                 "0.17.1",   require: false
+  gem "simplecov",                 "0.21.2",   require: false
   gem "simplecov-rcov",            "0.2.3",    require: false
 
   # test helpers
diff --git a/Gemfile.lock b/Gemfile.lock
index 778a90a..360ef3d 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -49,7 +49,7 @@ GEM
       safe_yaml (~> 1.0.0)
     crass (1.0.5)
     diff-lcs (1.3)
-    docile (1.3.2)
+    docile (1.4.0)
     erubi (1.9.0)
     ethon (0.12.0)
       ffi (>= 1.3.0)
@@ -82,7 +82,6 @@ GEM
       multi_xml (>= 0.5.2)
     i18n (1.7.0)
       concurrent-ruby (~> 1.0)
-    json (2.2.0)
     json-schema (2.8.1)
       addressable (>= 2.4)
     json-schema-rspec (0.0.4)
@@ -199,13 +198,14 @@ GEM
     sawyer (0.8.2)
       addressable (>= 2.3.5)
       faraday (> 0.8, < 2.0)
-    simplecov (0.17.1)
+    simplecov (0.21.2)
       docile (~> 1.1)
-      json (>= 1.8, < 3)
-      simplecov-html (~> 0.10.0)
-    simplecov-html (0.10.2)
+      simplecov-html (~> 0.11)
+      simplecov_json_formatter (~> 0.1)
+    simplecov-html (0.12.3)
     simplecov-rcov (0.2.3)
       simplecov (>= 0.4.1)
+    simplecov_json_formatter (0.1.3)
     systemu (2.6.5)
     terminal-table (1.8.0)
       unicode-display_width (~> 1.1, >= 1.1.1)
@@ -249,7 +249,7 @@ DEPENDENCIES
   rspec-rails (~> 3.9.0)
   rubocop (= 1.18.0)
   rubocop-rails (= 2.11.1)
-  simplecov (= 0.17.1)
+  simplecov (= 0.21.2)
   simplecov-rcov (= 0.2.3)
   webmock (~> 3.0)
   yard