diff --git a/Gemfile b/Gemfile
index 8347210..a4b5437 100644
--- a/Gemfile
+++ b/Gemfile
@@ -5,7 +5,7 @@ source "https://rubygems.org"
 git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }
 
 group :test do
-  gem "simplecov", "~> 0.17.1"
+  gem "simplecov", "~> 0.21.2"
   gem "simplecov-rcov", "~> 0.2.3"
   gem "rake", "~> 13.0"
   gem "test-unit", "~> 3.3"
diff --git a/Gemfile.lock b/Gemfile.lock
index 162e0d6..38ad689 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,17 +1,17 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    docile (1.3.2)
-    json (2.3.1)
+    docile (1.3.4)
     power_assert (1.1.5)
     rake (13.0.0)
-    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 (0.1.2)
     test-unit (3.3.4)
       power_assert
 
@@ -20,7 +20,7 @@ PLATFORMS
 
 DEPENDENCIES
   rake (~> 13.0)
-  simplecov (~> 0.17.1)
+  simplecov (~> 0.21.2)
   simplecov-rcov (~> 0.2.3)
   test-unit (~> 3.3)