diff --git a/forty_jekyll_theme.gemspec b/forty_jekyll_theme.gemspec
index 2a20494..ae3ea8f 100644
--- a/forty_jekyll_theme.gemspec
+++ b/forty_jekyll_theme.gemspec
@@ -12,6 +12,6 @@ Gem::Specification.new do |spec|
 
   spec.files         = `git ls-files -z`.split("\x0").select { |f| f.match(%r{^(assets|_layouts|_includes|_sass|LICENSE|README)}i) }
 
-  spec.add_development_dependency "jekyll", "~> 3.3"
+  spec.add_development_dependency "jekyll", "~> 4.0"
   spec.add_development_dependency "bundler", "~> 1.12"
 end