diff --git a/lib/async/http/faraday/clients.rb b/lib/async/http/faraday/clients.rb
index 3e8d1a8..b9e5c54 100644
--- a/lib/async/http/faraday/clients.rb
+++ b/lib/async/http/faraday/clients.rb
@@ -177,10 +177,10 @@ def with_proxied_client(proxy_endpoint, endpoint, &block)
 				# This will close all clients associated with all threads.
 				def close
 					Thread.list.each do |thread|
-						if clients = thread[@key]
-							clients.close
+						if clients = thread.thread_variable_get(@key)
+							thread.thread_variable_set(@key, nil)
 							
-							thread[@key] = nil
+							clients.close
 						end
 					end
 				end
diff --git a/releases.md b/releases.md
index 0ac1a16..142e418 100644
--- a/releases.md
+++ b/releases.md
@@ -1,5 +1,9 @@
 # Releases
 
+## Unreleased
+
+  - Fix memory leak in `Async::HTTP::Faraday::PerThreadPersistentClients` by ensuring that the `close` method is called on all clients when the adapter is closed.
+
 ## v0.21.0
 
 ### Improved support for `timeout` and `read_timeout`.
diff --git a/test/async/http/faraday/clients.rb b/test/async/http/faraday/clients.rb
index a4a90e6..1adc526 100644
--- a/test/async/http/faraday/clients.rb
+++ b/test/async/http/faraday/clients.rb
@@ -57,4 +57,33 @@
 			end
 		end
 	end
+	
+	with "#close" do
+		it "closes all clients" do
+			endpoint = Async::HTTP::Endpoint.parse("http://example.com")
+			client = clients.make_client(endpoint)
+			expect(client).to receive(:close)
+			
+			clients.close
+		end
+	end
+end
+
+describe Async::HTTP::Faraday::PerThreadPersistentClients do
+	let(:clients) {subject.new}
+	
+	with "#close" do
+		it "closes all clients" do
+			endpoint = Async::HTTP::Endpoint.parse("http://example.com")
+			closed = false
+			
+			clients.with_client(endpoint) do |client|
+				expect(client).to receive(:close, &proc{closed = true})
+			end
+			
+			expect(closed).to be == false
+			clients.close
+			expect(closed).to be == true
+		end
+	end
 end