diff --git a/src/Identity/S3/S3ExpressIdentityProvider.php b/src/Identity/S3/S3ExpressIdentityProvider.php
index 007968b33d..100bc228ab 100644
--- a/src/Identity/S3/S3ExpressIdentityProvider.php
+++ b/src/Identity/S3/S3ExpressIdentityProvider.php
@@ -23,22 +23,20 @@ public function __construct(string $clientRegion, array $config = [])
 
     public function __invoke($command)
     {
-        return function () use ($command) {
-            $bucket = $command['Bucket'];
-            if ($identity = $this->cache->get($bucket)) {
-                if (!$identity->isExpired()) {
-                    return Promise\Create::promiseFor($identity);
-                }
+        $bucket = $command['Bucket'];
+        if ($identity = $this->cache->get($bucket)) {
+            if (!$identity->isExpired()) {
+                return Promise\Create::promiseFor($identity);
             }
-            $response = $this->s3Client->createSession(['Bucket' => $bucket]);
-            $identity = new Aws\Identity\S3\S3ExpressIdentity(
-                $response['Credentials']['AccessKeyId'],
-                $response['Credentials']['SecretAccessKey'],
-                $response['Credentials']['SessionToken'],
-                $response['Credentials']['Expiration']->getTimestamp()
-            );
-            $this->cache->set($bucket, $identity);
-            return Promise\Create::promiseFor($identity);
-        };
+        }
+        $response = $this->s3Client->createSession(['Bucket' => $bucket]);
+        $identity = new Aws\Identity\S3\S3ExpressIdentity(
+            $response['Credentials']['AccessKeyId'],
+            $response['Credentials']['SecretAccessKey'],
+            $response['Credentials']['SessionToken'],
+            $response['Credentials']['Expiration']->getTimestamp()
+        );
+        $this->cache->set($bucket, $identity);
+        return Promise\Create::promiseFor($identity);
     }
 }
diff --git a/src/Middleware.php b/src/Middleware.php
index 3a779e47b0..dec46c096b 100644
--- a/src/Middleware.php
+++ b/src/Middleware.php
@@ -147,7 +147,7 @@ function (TokenInterface $token)
                 }
 
                 if ($signer instanceof S3ExpressSignature) {
-                    $credentialPromise = $config['s3_express_identity_provider']($command)();
+                    $credentialPromise = $config['s3_express_identity_provider']($command);
                 } else {
                     $credentialPromise = $credProvider();
                 }
diff --git a/src/S3/S3Client.php b/src/S3/S3Client.php
index 99e048b24e..c4e239c959 100644
--- a/src/S3/S3Client.php
+++ b/src/S3/S3Client.php
@@ -516,7 +516,7 @@ public function createPresignedRequest(CommandInterface $command, $expires, arra
         );
         if ($signature_version == 'v4-s3express') {
             $provider = $this->getConfig('s3_express_identity_provider');
-            $credentials = $provider($command)()->wait();
+            $credentials = $provider($command)->wait();
         } else {
             $credentials = $this->getCredentials()->wait();
         }
diff --git a/tests/Identity/S3Express/S3ExpressIdentityProviderTest.php b/tests/Identity/S3Express/S3ExpressIdentityProviderTest.php
index 66ba98efdd..54d96ab904 100644
--- a/tests/Identity/S3Express/S3ExpressIdentityProviderTest.php
+++ b/tests/Identity/S3Express/S3ExpressIdentityProviderTest.php
@@ -45,7 +45,7 @@ public function testProvidesIdentity()
             'region',
             ['client' => $client]
         );
-        $identity = $provider($cmd)()->wait();
+        $identity = $provider($cmd)->wait();
         self::assertSame('foo', $identity->getAccessKeyId());
         self::assertSame('bar', $identity->getSecretKey());
         self::assertSame('baz', $identity->getSecurityToken());
@@ -65,8 +65,8 @@ public function testCachesIdentity()
             'region',
             ['client' => $client]
         );
-        $provider($cmd)()->wait();
-        $identity = $provider($cmd)()->wait();
+        $provider($cmd)->wait();
+        $identity = $provider($cmd)->wait();
         self::assertSame('foo', $identity->getAccessKeyId());
         self::assertSame('bar', $identity->getSecretKey());
         self::assertSame('baz', $identity->getSecurityToken());
@@ -88,8 +88,8 @@ public function testRefreshesCache()
             'region',
             ['client' => $client]
         );
-        $provider($cmd)()->wait();
-        $identity = $provider($cmd)()->wait();
+        $provider($cmd)->wait();
+        $identity = $provider($cmd)->wait();
         self::assertSame($after, $identity->getExpiration());
     }
 }
diff --git a/tests/S3/S3ClientTest.php b/tests/S3/S3ClientTest.php
index 3df9a2938c..cf54918ad3 100644
--- a/tests/S3/S3ClientTest.php
+++ b/tests/S3/S3ClientTest.php
@@ -1229,15 +1229,13 @@ public function testS3ExpressAuth()
         $client = new S3Client([
             'region' => 'us-east-1',
             's3_express_identity_provider' => function ($command) {
-                return static function () {
-                    $identity = new S3ExpressIdentity(
-                        'foo',
-                        'bar',
-                        'baz',
-                         time() + 4000
-                    );
-                    return Promise\Create::promiseFor($identity);
-                };
+                $identity = new S3ExpressIdentity(
+                    'foo',
+                    'bar',
+                    'baz',
+                     time() + 4000
+                );
+                return Promise\Create::promiseFor($identity);
             },
             'http_handler' => function (RequestInterface $r) {
                 $this->assertSame('baz', $r->getHeaderLine('x-amz-s3session-token'));
@@ -1302,15 +1300,13 @@ public function testS3ExpressPresignedUrl()
             'version' => 'latest',
             'region' => 'us-east-1',
             's3_express_identity_provider' => function ($command) {
-                return static function () {
-                    $identity = new S3ExpressIdentity(
-                        'foo',
-                        'bar',
-                        'baz',
-                        time() + 4000
-                    );
-                    return Promise\Create::promiseFor($identity);
-                };
+                $identity = new S3ExpressIdentity(
+                    'foo',
+                    'bar',
+                    'baz',
+                    time() + 4000
+                );
+                return Promise\Create::promiseFor($identity);
             },
         ]);
         $client->getHandlerList()->appendBuild(