diff --git a/.rubocop.yml b/.rubocop.yml
index 00faa63..17b67f6 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -9,3 +9,6 @@ Metrics/ClassLength:
   Max: 110
 Metrics/ModuleLength:
   Max: 110
+Metrics/BlockLength:
+  Exclude:
+    - "googleauth.gemspec"
diff --git a/README.md b/README.md
index bb112de..f6d5db9 100644
--- a/README.md
+++ b/README.md
@@ -184,7 +184,7 @@ Custom storage implementations can also be used. See
 
 ## Supported Ruby Versions
 
-This library is currently supported on Ruby 1.9+.
+This library is currently supported on Ruby 2.3+.
 
 However, Ruby 2.4 or later is strongly recommended, as earlier releases have
 reached or are nearing end-of-life. After March 31, 2019, Google will provide
diff --git a/googleauth.gemspec b/googleauth.gemspec
index 5605b94..5513f8a 100755
--- a/googleauth.gemspec
+++ b/googleauth.gemspec
@@ -25,6 +25,7 @@ Gem::Specification.new do |gem|
   end
   gem.require_paths = ["lib"]
   gem.platform      = Gem::Platform::RUBY
+  gem.required_ruby_version = ">= 2.3.0"
 
   gem.add_dependency "faraday", "~> 0.12"
   gem.add_dependency "jwt", ">= 1.4", "< 3.0"