diff --git a/Gemfile.lock b/Gemfile.lock
index abfc197..be300ab 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -184,7 +184,7 @@ DEPENDENCIES
   github_changelog_generator
   pry-byebug
   rspec-rails (~> 3.8.0)
-  simplecov
+  simplecov (~> 0.17.1)
 
 BUNDLED WITH
    1.17.3
diff --git a/defra_ruby_mocks.gemspec b/defra_ruby_mocks.gemspec
index 0fc52ee..791b9f6 100644
--- a/defra_ruby_mocks.gemspec
+++ b/defra_ruby_mocks.gemspec
@@ -36,5 +36,5 @@ Gem::Specification.new do |s|
   s.add_development_dependency "defra_ruby_style"
   s.add_development_dependency "pry-byebug"
   s.add_development_dependency "rspec-rails", "~> 3.8.0"
-  s.add_development_dependency "simplecov"
+  s.add_development_dependency "simplecov", "~> 0.17.1"
 end