diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
index 4b833d945fe29f2861b976a15df222ed6562d5f1..98dca9e3c2d7894768eb2ed7e4b940b2cb1a0d91 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
@@ -835,7 +835,11 @@ def checkout_for_exclusive_access(checkout_timeout)
         end
 
         def with_new_connections_blocked
-          synchronize do
+          if defined?(JRUBY_VERSION)
+            synchronize do
+              @threads_blocking_new_connections += 1
+            end
+          else
             @threads_blocking_new_connections += 1
           end