diff --git a/src/Guzzle/MiddlewareFactory.php b/src/Guzzle/MiddlewareFactory.php
index 06839c4..8843ae6 100644
--- a/src/Guzzle/MiddlewareFactory.php
+++ b/src/Guzzle/MiddlewareFactory.php
@@ -53,7 +53,23 @@ public function retry( $delay = true ) {
 	 * @return callable
 	 */
 	private function getRetryDelay() {
-		return function( $numberOfRetries ) {
+		return function( $numberOfRetries, Response $response = null ) {
+			// The $response argument is only passed as of Guzzle 6.2.2.
+			if( $response !== null ) {
+				// Retry-After may be a number of seconds or an absolute date (RFC 7231,
+				// section 7.1.3).
+				$retryAfter = $response->getHeaderLine( 'Retry-After' );
+
+				if( is_numeric( $retryAfter ) ) {
+					return 1000 * $retryAfter;
+				}
+
+				if( $retryAfter ) {
+					$seconds = strtotime( $retryAfter ) - time();
+					return 1000 * max( 1, $seconds );
+				}
+			}
+
 			return 1000 * $numberOfRetries;
 		};
 	}
@@ -81,7 +97,6 @@ private function newRetryDecider() {
 			}
 
 			if( $response ) {
-				$headers = $response->getHeaders();
 				$data = json_decode( $response->getBody(), true );
 
 				// Retry on server errors
@@ -89,30 +104,33 @@ private function newRetryDecider() {
 					$shouldRetry = true;
 				}
 
-				if ( array_key_exists( 'mediawiki-api-error', $headers ) ) {
-					foreach( $headers['mediawiki-api-error'] as $mediawikiApiErrorHeader ) {
-						if (
-							// Retry if we have a response with an API error worth retrying
-							in_array(
-								$mediawikiApiErrorHeader,
-								array(
-									'ratelimited',
-									'readonly',
-									'internal_api_error_DBQueryError',
-								)
-							)
-							||
-							// Or if we have been stopped from saving as an 'anti-abuse measure'
-							// Note: this tries to match "actionthrottledtext" i18n messagae for mediawiki
-							(
-								$mediawikiApiErrorHeader == 'failed-save' &&
-								strstr( $data['error']['info'], 'anti-abuse measure' )
+				foreach( $response->getHeader( 'Mediawiki-Api-Error' ) as $mediawikiApiErrorHeader ) {
+					if (
+						// Retry if the API explicitly tells us to:
+						// https://www.mediawiki.org/wiki/Manual:Maxlag_parameter
+						$response->getHeaderLine( 'Retry-After' )
+						||
+						// Retry if we have a response with an API error worth retrying
+						in_array(
+							$mediawikiApiErrorHeader,
+							array(
+								'ratelimited',
+								'maxlag',
+								'readonly',
+								'internal_api_error_DBQueryError',
 							)
-						) {
-							$shouldRetry = true;
-						}
-
+						)
+						||
+						// Or if we have been stopped from saving as an 'anti-abuse measure'
+						// Note: this tries to match "actionthrottledtext" i18n messagae for mediawiki
+						(
+							$mediawikiApiErrorHeader == 'failed-save' &&
+							strstr( $data['error']['info'], 'anti-abuse measure' )
+						)
+					) {
+						$shouldRetry = true;
 					}
+
 				}
 			}
 
diff --git a/tests/unit/Guzzle/MiddlewareFactoryTest.php b/tests/unit/Guzzle/MiddlewareFactoryTest.php
index a2ef078..73bf2cf 100644
--- a/tests/unit/Guzzle/MiddlewareFactoryTest.php
+++ b/tests/unit/Guzzle/MiddlewareFactoryTest.php
@@ -20,66 +20,52 @@
 class MiddlewareFactoryTest extends \PHPUnit_Framework_TestCase {
 
 	public function testRetriesConnectException() {
-		$middlewareFactory = new MiddlewareFactory();
-
-		$mock = new MockHandler(
-			array(
-				new ConnectException( "Error 1", new Request( 'GET', 'test' ) ),
-				new Response( 200, [ 'X-Foo' => 'Bar' ] ),
-			)
-		);
+		$queue = [
+			new ConnectException( 'Error 1', new Request( 'GET', 'test' ) ),
+			new Response( 200, [ 'X-Foo' => 'Bar' ] ),
+		];
 
-		$handler = HandlerStack::create( $mock );
-		$handler->push( $middlewareFactory->retry( false ) );
-		$client = new Client( [ 'handler' => $handler ] );
+		$client = $this->getClient( $queue, $delays );
+		$response = $client->request( 'GET', '/' );
 
-		$this->assertEquals( 200, $client->request( 'GET', '/' )->getStatusCode() );
+		$this->assertEquals( 200, $response->getStatusCode() );
+		$this->assertEquals( [ 1000 ], $delays );
 	}
 
 	public function testRetries500Errors() {
-		$middlewareFactory = new MiddlewareFactory();
-
-		$mock = new MockHandler(
-			array(
-				new Response( 500 ),
-				new Response( 200 ),
-			)
-		);
+		$queue = [
+			new Response( 500 ),
+			new Response( 200 ),
+		];
 
-		$handler = HandlerStack::create( $mock );
-		$handler->push( $middlewareFactory->retry( false ) );
-		$client = new Client( [ 'handler' => $handler ] );
+		$client = $this->getClient( $queue, $delays );
+		$response = $client->request( 'GET', '/' );
 
-		$this->assertEquals( 200, $client->request( 'GET', '/' )->getStatusCode() );
+		$this->assertEquals( 200, $response->getStatusCode() );
+		$this->assertEquals( [ 1000 ], $delays );
 	}
 
 	public function testRetriesSomeMediawikiApiErrorHeaders() {
-		$middlewareFactory = new MiddlewareFactory();
-
-		$mock = new MockHandler(
-			array(
-				new Response( 200, array( 'mediawiki-api-error' => 'ratelimited' ) ),
-				new Response( 200, array( 'mediawiki-api-error' => 'readonly' ) ),
-				new Response( 200, array( 'mediawiki-api-error' => 'internal_api_error_DBQueryError' ) ),
-				new Response( 200, array( 'mediawiki-api-error' => 'DoNotRetryThisHeader' ) ),
-			)
-		);
-
-		$handler = HandlerStack::create( $mock );
-		$handler->push( $middlewareFactory->retry( false ) );
-		$client = new Client( [ 'handler' => $handler ] );
-
+		$queue = [
+			new Response( 200, array( 'mediawiki-api-error' => 'ratelimited' ) ),
+			new Response( 200, array( 'mediawiki-api-error' => 'maxlag' ) ),
+			new Response( 200, array( 'mediawiki-api-error' => 'readonly' ) ),
+			new Response( 200, array( 'mediawiki-api-error' => 'internal_api_error_DBQueryError' ) ),
+			new Response( 200, array( 'mediawiki-api-error' => 'DoNotRetryThisHeader' ) ),
+		];
+
+		$client = $this->getClient( $queue, $delays );
 		$response = $client->request( 'GET', '/' );
+
 		$this->assertEquals( 200, $response->getStatusCode() );
 		$this->assertEquals(
 			array( 'DoNotRetryThisHeader' ),
 			$response->getHeader( 'mediawiki-api-error' )
 		);
+		$this->assertEquals( [ 1000, 2000, 3000, 4000 ], $delays );
 	}
 
 	public function testRetryAntiAbuseMeasure() {
-		$middlewareFactory = new MiddlewareFactory();
-
 		$antiAbusejson = json_encode(
 			array(
 				'error' => array(
@@ -88,71 +74,142 @@ public function testRetryAntiAbuseMeasure() {
 			)
 		);
 
-		$mock = new MockHandler(
-			array(
-				new Response( 200, array( 'mediawiki-api-error' => 'failed-save' ), $antiAbusejson ),
-				new Response( 200, array( 'mediawiki-api-error' => 'DoNotRetryThisHeader' ) ),
-			)
-		);
-
-		$handler = HandlerStack::create( $mock );
-		$handler->push( $middlewareFactory->retry( false ) );
-		$client = new Client( [ 'handler' => $handler ] );
+		$queue = [
+			new Response( 200, array( 'mediawiki-api-error' => 'failed-save' ), $antiAbusejson ),
+			new Response( 200, array( 'mediawiki-api-error' => 'DoNotRetryThisHeader' ) ),
+		];
 
+		$client = $this->getClient( $queue, $delays );
 		$response = $client->request( 'GET', '/' );
-		$this->assertSame( 200, $response->getStatusCode() );
-		$this->assertEquals(
-			array( 'DoNotRetryThisHeader' ),
-			$response->getHeader( 'mediawiki-api-error' )
-		);
+
+		$this->assertEquals( 200, $response->getStatusCode() );
+		$this->assertEquals( 'DoNotRetryThisHeader', $response->getHeaderLine( 'mediawiki-api-error' ) );
 	}
 
 	public function testRetryLimit() {
-		$middlewareFactory = new MiddlewareFactory();
-
-		$mock = new MockHandler(
-			array(
-				new ConnectException( "Error 1", new Request( 'GET', 'test' ) ),
-				new ConnectException( "Error 2", new Request( 'GET', 'test' ) ),
-				new ConnectException( "Error 3", new Request( 'GET', 'test' ) ),
-				new ConnectException( "Error 4", new Request( 'GET', 'test' ) ),
-				new ConnectException( "Error 5", new Request( 'GET', 'test' ) ),
-				new ConnectException( "Error 6", new Request( 'GET', 'test' ) ),
-			)
-		);
-
-		$handler = HandlerStack::create( $mock );
-		$handler->push( $middlewareFactory->retry( false ) );
-		$client = new Client( [ 'handler' => $handler ] );
+		$queue = [
+			new ConnectException( 'Error 1', new Request( 'GET', 'test' ) ),
+			new ConnectException( 'Error 2', new Request( 'GET', 'test' ) ),
+			new ConnectException( 'Error 3', new Request( 'GET', 'test' ) ),
+			new ConnectException( 'Error 4', new Request( 'GET', 'test' ) ),
+			new ConnectException( 'Error 5', new Request( 'GET', 'test' ) ),
+			new ConnectException( 'Error 6', new Request( 'GET', 'test' ) ),
+			new Response( 200 ),
+		];
+
+		$client = $this->getClient( $queue );
 
 		$this->setExpectedException(
 			'GuzzleHttp\Exception\ConnectException',
 			'Error 6'
 		);
 
-		$client->request( 'GET', '/' )->getStatusCode();
+		$client->request( 'GET', '/' );
 	}
 
-	public function testRetryDelay() {
-		$middlewareFactory = new MiddlewareFactory();
+	public function testConnectExceptionRetryDelay() {
+		$queue = [
+			new ConnectException( '+1 second delay', new Request( 'GET', 'test' ) ),
+			new ConnectException( '+2 second delay', new Request( 'GET', 'test' ) ),
+			new Response( 200 ),
+		];
 
-		$mock = new MockHandler(
-			array(
-				new ConnectException( "+1 second delay", new Request( 'GET', 'test' ) ),
-				new ConnectException( "+2 second delay", new Request( 'GET', 'test' ) ),
-				new Response( 200 ),
-			)
-		);
+		$client = $this->getClient( $queue, $delays );
+		$response = $client->request( 'GET', '/' );
+
+		$this->assertEquals( 200, $response->getStatusCode() );
+		$this->assertEquals( [ 1000, 2000 ], $delays );
+	}
+
+	public function testServerErrorRetryDelay() {
+		$queue = [
+			new Response( 500 ),
+			new Response( 503 ),
+			new Response( 200 ),
+		];
+
+		$client = $this->getClient( $queue, $delays );
+		$response = $client->request( 'GET', '/' );
+
+		$this->assertEquals( 200, $response->getStatusCode() );
+		$this->assertEquals( [ 1000, 2000 ], $delays );
+	}
+
+	public function testRelativeRetryDelayHeaderRetryDelay() {
+		$queue = [
+			new Response( 200, [ 'mediawiki-api-error' => 'maxlag', 'retry-after' => 10 ] ),
+			new Response( 200 ),
+		];
+
+		$this->getClient( $queue, $delays )->request( 'GET', '/' );
+
+		$this->assertEquals( [ 10000 ], $delays );
+	}
+
+	public function testAbsoluteRetryDelayHeaderRetryDelay() {
+		$queue = [
+			new Response(
+				200,
+				[
+					'mediawiki-api-error' => 'maxlag',
+					'retry-after' => gmdate( DATE_RFC1123, time() + 600 ),
+				]
+			),
+			new Response( 200 ),
+		];
+
+		$client = $this->getClient( $queue, $delays );
+		$response = $client->request( 'GET', '/' );
+
+		$this->assertEquals( 200, $response->getStatusCode() );
+		$this->assertCount( 1, $delays );
+		// Allow 5 second delay while running this test.
+		$this->assertGreaterThan( 600000 - 5000 , $delays[0] );
+	}
+
+	public function testPastRetryDelayHeaderRetryDelay() {
+		$queue = [
+			new Response(
+				200,
+				[
+					'mediawiki-api-error' => 'maxlag',
+					'retry-after' => 'Fri, 31 Dec 1999 23:59:59 GMT',
+				]
+			),
+			new Response( 200 ),
+		];
+
+		$client = $this->getClient( $queue, $delays );
+		$response = $client->request( 'GET', '/' );
+
+		$this->assertEquals( 200, $response->getStatusCode() );
+		$this->assertEquals( [ 1000 ] , $delays );
+	}
+
+	private function getClient( array $queue, &$delays = null ) {
+		$mock = new MockHandler( $queue );
 
 		$handler = HandlerStack::create( $mock );
-		$handler->push( $middlewareFactory->retry( true ) );
-		$client = new Client( [ 'handler' => $handler ] );
 
-		$startTime = time();
-		$client->request( 'GET', '/' )->getStatusCode();
-		$endTime = time();
+		$middlewareFactory = new MiddlewareFactory();
+		$handler->push( $middlewareFactory->retry() );
+
+		$delayMocker = $this->getDelayMocker( $delays );
+		$handler->push( $delayMocker );
 
-		$this->assertGreaterThan( $startTime + 2, $endTime );
+		return new Client( [ 'handler' => $handler ] );
 	}
 
+	private function getDelayMocker( &$delays ) {
+		return function( callable $handler) use ( &$delays ) {
+			return function( $request, array $options ) use ( $handler, &$delays ) {
+				if( isset( $options['delay'] ) ) {
+					$delays[] = $options['delay'];
+					unset( $options['delay'] );
+				}
+				return $handler( $request, $options );
+			};
+		};
+
+	}
 }