diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8ebb6cf4..dfe84b3b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@ appear at the top.
 ## [Unreleased][]
 
   * Your contribution here!
+  * [#447](https://github.com/capistrano/sshkit/pull/447): Fix broken thread safety by widening critical section - [Takumasa Ochi](https://github.com/aeroastro)
 
 ## [1.18.0][] (2018-10-21)
 
diff --git a/lib/sshkit/backends/connection_pool.rb b/lib/sshkit/backends/connection_pool.rb
index c7cd4675..37d69eeb 100644
--- a/lib/sshkit/backends/connection_pool.rb
+++ b/lib/sshkit/backends/connection_pool.rb
@@ -118,9 +118,9 @@ def thread_safe_find_or_create_cache(key)
   # Update cache key with changed args to prevent cache miss
   def update_key_if_args_changed(cache, args)
     new_key = cache_key_for_connection_args(args)
-    return if cache.same_key?(new_key)
 
     caches.synchronize do
+      return if cache.same_key?(new_key)
       caches[new_key] = caches.delete(cache.key)
       cache.key = new_key
     end