diff --git a/Rakefile b/Rakefile
index 99404937..39e9782e 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,6 +1,5 @@
 require "bundler/gem_tasks"
 require "rspec/core/rake_task"
-require "jasmine"
 
 RSpec::Core::RakeTask.new(:spec)
 
diff --git a/govuk_tech_docs.gemspec b/govuk_tech_docs.gemspec
index 4a1650d1..7c103a7d 100644
--- a/govuk_tech_docs.gemspec
+++ b/govuk_tech_docs.gemspec
@@ -39,6 +39,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency "base64" # TODO: remove once middleman-sprockets declares this itself.
   spec.add_dependency "bigdecimal" # TODO: remove once activesupport declares this itself.
   spec.add_dependency "chronic", "~> 0.10.2"
+  spec.add_dependency "concurrent-ruby", "1.3.4" # 1.3.5 introduced a change that breaks activesupport, and so middleman
   spec.add_dependency "csv" # TODO: remove once tilt declares this itself.
   spec.add_dependency "haml", "~> 6.0"
   spec.add_dependency "middleman", "~> 4.0"
@@ -57,7 +58,6 @@ Gem::Specification.new do |spec|
 
   spec.add_development_dependency "byebug"
   spec.add_development_dependency "capybara", "~> 3.32"
-  spec.add_development_dependency "jasmine", "~> 3.5"
   spec.add_development_dependency "rake", "~> 13.0"
   spec.add_development_dependency "rspec", "~> 3.9"
   spec.add_development_dependency "rubocop-govuk", "~> 4.10"