diff --git a/Gemfile b/Gemfile
index 1bcc0b9..cc9182e 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,7 +1,7 @@
 source 'https://rubygems.org'
 
 gem 'byebug'
-gem 'json', '~> 2.4.0'
+gem 'json', '~> 2.3.0'
 gem 'rubocop', '~> 0.51.0', require: false
 gem 'hex_string'
 gem 'number-theory'
diff --git a/Gemfile.lock b/Gemfile.lock
index f01007e..938d998 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -3,9 +3,8 @@ GEM
   specs:
     ast (2.4.0)
     byebug (10.0.2)
-    gcd (0.0.1)
     hex_string (1.0.1)
-    json (2.1.0)
+    json (2.3.0)
     narray (0.6.1.2)
     number-theory (1.0.0)
       narray (>= 0.6)
@@ -15,7 +14,7 @@ GEM
     powerpack (0.1.2)
     rainbow (2.2.2)
       rake
-    rake (12.3.1)
+    rake (13.0.3)
     rubocop (0.51.0)
       parallel (~> 1.10)
       parser (>= 2.3.3.1, < 3.0)
@@ -31,10 +30,10 @@ PLATFORMS
 
 DEPENDENCIES
   byebug
-  gcd
   hex_string
-  json (~> 2.1.0)
+  json (~> 2.3.0)
   number-theory
+  rake (>= 12.3.3)
   rubocop (~> 0.51.0)
 
 BUNDLED WITH