diff --git a/.changes/nextrelease/s3-region-fix.json b/.changes/nextrelease/s3-region-fix.json
new file mode 100644
index 0000000000..3f7544de1b
--- /dev/null
+++ b/.changes/nextrelease/s3-region-fix.json
@@ -0,0 +1,7 @@
+[
+  {
+    "type": "bugfix",
+    "category": "S3",
+    "description": "Fixes warning in S3 client when region is not provided in constructor"
+  }
+]
diff --git a/src/S3/S3Client.php b/src/S3/S3Client.php
index da0e1dfe39..88de7473f7 100644
--- a/src/S3/S3Client.php
+++ b/src/S3/S3Client.php
@@ -801,9 +801,18 @@ private function processEndpointV2Model()
      */
     private function addBuiltIns($args)
     {
-        if ($args['region'] !== 'us-east-1') {
+        if (isset($args['region'])
+            && $args['region'] !== 'us-east-1'
+        ) {
+            return false;
+        }
+
+        if (!isset($args['region'])
+            && ConfigurationResolver::resolve('region', '', 'string') !== 'us-east-1'
+        ) {
             return false;
         }
+
         $key = 'AWS::S3::UseGlobalEndpoint';
         $result = $args['s3_us_east_1_regional_endpoint'] instanceof \Closure ?
             $args['s3_us_east_1_regional_endpoint']()->wait() : $args['s3_us_east_1_regional_endpoint'];
diff --git a/tests/S3/S3ClientTest.php b/tests/S3/S3ClientTest.php
index 9b4f0d64e3..7eddeebfc6 100644
--- a/tests/S3/S3ClientTest.php
+++ b/tests/S3/S3ClientTest.php
@@ -1,7 +1,6 @@
 <?php
 namespace Aws\Test\S3;
 
-use Aws\Arn\ArnParser;
 use Aws\Command;
 use Aws\CommandInterface;
 use Aws\Exception\AwsException;
@@ -15,7 +14,6 @@
 use Aws\S3\RegionalEndpoint\Configuration;
 use Aws\S3\S3Client;
 use Aws\S3\UseArnRegion\Configuration as UseArnRegionConfiguration;
-use Aws\Signature\SignatureV4;
 use Aws\Test\UsesServiceTrait;
 use GuzzleHttp\Exception\ConnectException;
 use GuzzleHttp\Exception\RequestException;
@@ -25,7 +23,6 @@
 use GuzzleHttp\Psr7;
 use GuzzleHttp\Psr7\Response;
 use GuzzleHttp\Psr7\Uri;
-use http\Exception\InvalidArgumentException;
 use Psr\Http\Message\RequestInterface;
 use Yoast\PHPUnitPolyfills\TestCases\TestCase;
 use Aws\Exception\UnresolvedEndpointException;
@@ -2476,4 +2473,35 @@ public function dotSegmentPathStyleProvider()
         ];
     }
 
+    /**
+     * @dataProvider builtinRegionProvider
+     */
+    public function testCorrectlyResolvesGlobalEndpointWithoutRegionInConstructor(
+        $region, $expected
+    ){
+        putenv('AWS_REGION=' . $region);
+
+        $s3Client = new S3Client([]);
+        $builtIns = $s3Client->getClientBuiltIns();
+        //The UseGlobalEndpoint builtin should be set by default if
+        //the region provided is us-east-1.
+        $this->assertEquals($expected, isset($builtIns['AWS::S3::UseGlobalEndpoint']));
+
+        //When the UseGlobalEndpoint builtin is set (i.e. us-east-1 is the region)
+        // the default value should be `true`, unless `s3_us_east_1_regional_endpoint`
+        // is set to `regional`.
+        if ($expected) {
+            $this->assertEquals($expected, $builtIns['AWS::S3::UseGlobalEndpoint']);
+        }
+
+        putenv('AWS_REGION=');
+    }
+
+    public function builtinRegionProvider()
+    {
+        return [
+            ['us-east-1' , true],
+            ['us-west-2', false]
+        ];
+    }
 }