diff --git a/SnsProducer.php b/SnsProducer.php
index bbd46a9..3a6bd42 100644
--- a/SnsProducer.php
+++ b/SnsProducer.php
@@ -51,7 +51,7 @@ public function send(Destination $destination, Message $message): void
             'MessageAttributes' => [
                 'Headers' => [
                     'DataType' => 'String',
-                    'StringValue' => json_encode([$message->getHeaders(), $message->getProperties()]),
+                    'StringValue' => base64_encode(json_encode([$message->getHeaders(), $message->getProperties()])),
                 ],
             ],
             'TopicArn' => $topicArn,
diff --git a/Tests/SnsProducerTest.php b/Tests/SnsProducerTest.php
index 5f87849..07f5e23 100644
--- a/Tests/SnsProducerTest.php
+++ b/Tests/SnsProducerTest.php
@@ -138,7 +138,7 @@ public function testShouldPublish()
             'MessageAttributes' => [
                 'Headers' => [
                     'DataType' => 'String',
-                    'StringValue' => '[{"hkey":"hvaleu"},{"key":"value"}]',
+                    'StringValue' => base64_encode('[{"hkey":"hvaleu"},{"key":"value"}]'),
                 ],
             ],
             'TopicArn' => 'theTopicArn',
@@ -189,7 +189,7 @@ public function testShouldPublishWithMergedAttributes()
             'MessageAttributes' => [
                 'Headers' => [
                     'DataType' => 'String',
-                    'StringValue' => '[[],[]]',
+                    'StringValue' => base64_encode('[[],[]]'),
                 ],
                 'Foo' => [
                     'DataType' => 'String',