diff --git a/.circleci/config.yml b/.circleci/config.yml
index df9dac51..85f6f7cf 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -19,7 +19,7 @@ ruby-docker-template: &ruby-docker-template
           gem install jruby-openssl; # required by bundler, no effect on Ruby MRI
         fi
     - run: ruby -v
-    - run: gem install bundler
+    - run: gem install bundler -v "~> 1.7"
     - run: bundle install
     - run: mkdir ./rspec
     - run: bundle exec rspec --format progress --format RspecJunitFormatter -o ./rspec/rspec.xml spec
@@ -80,7 +80,7 @@ jobs:
               if [[ $i == jruby* ]]; then
                 gem install jruby-openssl; # required by bundler, no effect on Ruby MRI
               fi
-              gem install bundler;
+              gem install bundler -v "~> 1.7";
               bundle install;
               mv Gemfile.lock "Gemfile.lock.$i"
             done
diff --git a/.gitignore b/.gitignore
index bb576123..3f9d02f2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -12,5 +12,4 @@
 *.a
 mkmf.log
 *.gem
-Gemfile.lock
 .DS_Store
diff --git a/Gemfile.lock b/Gemfile.lock
new file mode 100644
index 00000000..6c4673e4
--- /dev/null
+++ b/Gemfile.lock
@@ -0,0 +1,88 @@
+PATH
+  remote: .
+  specs:
+    ldclient-rb (5.4.1)
+      concurrent-ruby (~> 1.0)
+      faraday (>= 0.9, < 2)
+      faraday-http-cache (>= 1.3.0, < 3)
+      http_tools (~> 0.4.5)
+      json (>= 1.8, < 3)
+      net-http-persistent (~> 2.9)
+      semantic (~> 1.6)
+      socketry (~> 0.5.1)
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    codeclimate-test-reporter (0.6.0)
+      simplecov (>= 0.7.1, < 1.0.0)
+    concurrent-ruby (1.1.4)
+    connection_pool (2.2.1)
+    diff-lcs (1.3)
+    docile (1.1.5)
+    faraday (0.15.4)
+      multipart-post (>= 1.2, < 3)
+    faraday-http-cache (2.0.0)
+      faraday (~> 0.8)
+    ffi (1.9.25)
+    ffi (1.9.25-java)
+    hitimes (1.3.0)
+    hitimes (1.3.0-java)
+    http_tools (0.4.5)
+    json (1.8.6)
+    json (1.8.6-java)
+    listen (3.1.5)
+      rb-fsevent (~> 0.9, >= 0.9.4)
+      rb-inotify (~> 0.9, >= 0.9.7)
+      ruby_dep (~> 1.2)
+    multipart-post (2.0.0)
+    net-http-persistent (2.9.4)
+    rake (10.5.0)
+    rb-fsevent (0.10.3)
+    rb-inotify (0.9.10)
+      ffi (>= 0.5.0, < 2)
+    redis (3.3.5)
+    rspec (3.7.0)
+      rspec-core (~> 3.7.0)
+      rspec-expectations (~> 3.7.0)
+      rspec-mocks (~> 3.7.0)
+    rspec-core (3.7.1)
+      rspec-support (~> 3.7.0)
+    rspec-expectations (3.7.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.7.0)
+    rspec-mocks (3.7.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.7.0)
+    rspec-support (3.7.0)
+    rspec_junit_formatter (0.3.0)
+      rspec-core (>= 2, < 4, != 2.12.0)
+    ruby_dep (1.5.0)
+    semantic (1.6.1)
+    simplecov (0.15.1)
+      docile (~> 1.1.0)
+      json (>= 1.8, < 3)
+      simplecov-html (~> 0.10.0)
+    simplecov-html (0.10.2)
+    socketry (0.5.1)
+      hitimes (~> 1.2)
+    timecop (0.9.1)
+
+PLATFORMS
+  java
+  ruby
+
+DEPENDENCIES
+  bundler (~> 1.7)
+  codeclimate-test-reporter (~> 0)
+  connection_pool (>= 2.1.2)
+  ldclient-rb!
+  listen (~> 3.0)
+  rake (~> 10.0)
+  redis (~> 3.3.5)
+  rspec (~> 3.2)
+  rspec_junit_formatter (~> 0.3.0)
+  timecop (~> 0.9.1)
+
+BUNDLED WITH
+   1.17.3
diff --git a/ldclient-rb.gemspec b/ldclient-rb.gemspec
index 0b8f4f9d..46dac190 100644
--- a/ldclient-rb.gemspec
+++ b/ldclient-rb.gemspec
@@ -34,11 +34,9 @@ Gem::Specification.new do |spec|
   spec.add_runtime_dependency "json", [">= 1.8", "< 3"]
   spec.add_runtime_dependency "faraday", [">= 0.9", "< 2"]
   spec.add_runtime_dependency "faraday-http-cache", [">= 1.3.0", "< 3"]
-  spec.add_runtime_dependency "semantic", "~> 1.6.0"
-  spec.add_runtime_dependency "thread_safe", "~> 0.3"
+  spec.add_runtime_dependency "semantic", "~> 1.6"
   spec.add_runtime_dependency "net-http-persistent", "~> 2.9"
-  spec.add_runtime_dependency "concurrent-ruby", "~> 1.0.4"
-  spec.add_runtime_dependency "hashdiff", "~> 0.2"
+  spec.add_runtime_dependency "concurrent-ruby", "~> 1.0"
   spec.add_runtime_dependency "http_tools", '~> 0.4.5'
   spec.add_runtime_dependency "socketry", "~> 0.5.1"
 end
diff --git a/lib/ldclient-rb/cache_store.rb b/lib/ldclient-rb/cache_store.rb
index 0677da65..164534fb 100644
--- a/lib/ldclient-rb/cache_store.rb
+++ b/lib/ldclient-rb/cache_store.rb
@@ -1,12 +1,12 @@
-require "thread_safe"
+require "concurrent/map"
 
 module LaunchDarkly
-  # A thread-safe in-memory store suitable for use
-  # with the Faraday caching HTTP client. Uses the
-  # Threadsafe gem as the underlying cache.
+  #
+  # A thread-safe in-memory store suitable for use with the Faraday caching HTTP client. Uses the
+  # concurrent-ruby gem's Map as the underlying cache.
   #
   # @see https://github.com/plataformatec/faraday-http-cache
-  # @see https://github.com/ruby-concurrency/thread_safe
+  # @see https://github.com/ruby-concurrency
   #
   class ThreadSafeMemoryStore
     #
@@ -14,7 +14,7 @@ class ThreadSafeMemoryStore
     #
     # @return [ThreadSafeMemoryStore] a new store
     def initialize
-      @cache = ThreadSafe::Cache.new
+      @cache = Concurrent::Map.new
     end
 
     #
diff --git a/lib/ldclient-rb/redis_store.rb b/lib/ldclient-rb/redis_store.rb
index 3729ca6b..c9b1bc64 100644
--- a/lib/ldclient-rb/redis_store.rb
+++ b/lib/ldclient-rb/redis_store.rb
@@ -1,6 +1,5 @@
 require "concurrent/atomics"
 require "json"
-require "thread_safe"
 
 module LaunchDarkly
   #