diff --git a/src/Ganesha/GuzzleMiddleware.php b/src/Ganesha/GuzzleMiddleware.php
index ede16f4..1821c36 100644
--- a/src/Ganesha/GuzzleMiddleware.php
+++ b/src/Ganesha/GuzzleMiddleware.php
@@ -26,6 +26,20 @@ class GuzzleMiddleware
      */
     private $failureDetector;
 
+    /**
+     * Function name to be used for returning a rejected promise.
+     *
+     * @var string
+     */
+    private string $rejectionForFunction;
+
+    /**
+     * Function name to be used for returning a promise.
+     *
+     * @var string
+     */
+    private string $promiseForFunction;
+
     public function __construct(
         Ganesha $ganesha,
         ServiceNameExtractorInterface $serviceNameExtractor = null,
@@ -34,6 +48,16 @@ public function __construct(
         $this->ganesha = $ganesha;
         $this->serviceNameExtractor = $serviceNameExtractor ?: new ServiceNameExtractor();
         $this->failureDetector = $failureDetector ?: new AlwaysSuccessFailureDetector();
+
+        // We need to support both the static and function API of `guzzle/promises` for the time being.
+        // https://github.com/guzzle/promises#upgrading-from-function-api
+        if (class_exists('\GuzzleHttp\Promise\Create')) {
+            $this->rejectionForFunction = '\GuzzleHttp\Promise\Create::rejectionFor';
+            $this->promiseForFunction = '\GuzzleHttp\Promise\Create::promiseFor';
+        } else {
+            $this->rejectionForFunction = '\GuzzleHttp\Promise\rejection_for';
+            $this->promiseForFunction = '\GuzzleHttp\Promise\promise_for';
+        }
     }
 
     /**
@@ -46,7 +70,8 @@ public function __invoke(callable $handler): \Closure
             $serviceName = $this->serviceNameExtractor->extract($request, $options);
 
             if (!$this->ganesha->isAvailable($serviceName)) {
-                return \GuzzleHttp\Promise\rejection_for(
+                return call_user_func(
+                    $this->rejectionForFunction,
                     new RejectedException(
                         sprintf('"%s" is not available', $serviceName)
                     )
@@ -62,11 +87,17 @@ function ($value) use ($serviceName) {
                     } else {
                         $this->ganesha->success($serviceName);
                     }
-                    return \GuzzleHttp\Promise\promise_for($value);
+                    return call_user_func(
+                        $this->promiseForFunction,
+                        $value
+                    );
                 },
                 function ($reason) use ($serviceName) {
                     $this->ganesha->failure($serviceName);
-                    return \GuzzleHttp\Promise\rejection_for($reason);
+                    return call_user_func(
+                        $this->rejectionForFunction,
+                        $reason
+                    );
                 }
             );
         };