diff --git a/src/Api/Domain.php b/src/Api/Domain.php
index 1c2a19e..9bb767b 100644
--- a/src/Api/Domain.php
+++ b/src/Api/Domain.php
@@ -36,6 +36,7 @@ use Psr\Http\Message\ResponseInterface;
  */
 class Domain extends HttpApi
 {
+    private const DKIM_SIZES = ['1024', '2048'];
     /**
      * Returns a list of domains on the account.
      *
@@ -84,12 +85,13 @@ class Domain extends HttpApi
      * @param bool     $wildcard           domain will accept email for subdomains
      * @param bool     $forceDkimAuthority force DKIM authority
      * @param string[] $ips                an array of ips to be assigned to the domain
-     * @param ?string  $pool_id            pool id to assign to the domain
+     * @param ?string  $poolId             pool id to assign to the domain
      * @param string   $webScheme          `http` or `https` - set your open, click and unsubscribe URLs to use http or https. The default is http
+     * @param string   $dkimKeySize        Set length of your domain’s generated DKIM key
      *
      * @return CreateResponse|array|ResponseInterface
      */
-    public function create(string $domain, string $smtpPass = null, string $spamAction = null, bool $wildcard = null, bool $forceDkimAuthority = null, ?array $ips = null, ?string $pool_id = null, string $webScheme = 'http')
+    public function create(string $domain, string $smtpPass = null, string $spamAction = null, bool $wildcard = null, bool $forceDkimAuthority = null, ?array $ips = null, ?string $poolId = null, string $webScheme = 'http', string $dkimKeySize = '1024')
     {
         Assert::stringNotEmpty($domain);
 
@@ -133,10 +135,18 @@ class Domain extends HttpApi
             $params['web_scheme'] = $webScheme;
         }
 
-        if (null !== $pool_id) {
-            Assert::stringNotEmpty($pool_id);
+        if (null !== $poolId) {
+            Assert::stringNotEmpty($poolId);
 
-            $params['pool_id'] = $pool_id;
+            $params['pool_id'] = $poolId;
+        }
+        if (null !== $dkimKeySize) {
+            Assert::oneOf(
+                $dkimKeySize, 
+                self::DKIM_SIZES, 
+                'Length of your domain’s generated DKIM key must be 1024 or 2048'
+            );
+            $params['dkim_key_size'] = $dkimKeySize;
         }
 
         $response = $this->httpPost('/v3/domains', $params);
diff --git a/tests/Api/DomainTest.php b/tests/Api/DomainTest.php
index c4da5e5..3f4f019 100644
--- a/tests/Api/DomainTest.php
+++ b/tests/Api/DomainTest.php
@@ -83,6 +83,7 @@ JSON
         $this->setRequestBody([
             'name' => 'example.com',
             'web_scheme' => 'http',
+            'dkim_key_size' => '1024'
         ]);
         $this->setHydrateClass(CreateResponse::class);
 
@@ -98,6 +99,7 @@ JSON
             'name' => 'example.com',
             'smtp_password' => 'foo',
             'web_scheme' => 'http',
+            'dkim_key_size' => '1024'
         ]);
         $this->setHydrateClass(CreateResponse::class);
 
@@ -114,6 +116,7 @@ JSON
             'smtp_password' => 'foo',
             'pool_id' => '123',
             'web_scheme' => 'http',
+            'dkim_key_size' => '1024'
         ]);
         $this->setHydrateClass(CreateResponse::class);
 
@@ -130,6 +133,7 @@ JSON
             'smtp_password' => 'foo',
             'spam_action' => 'bar',
             'web_scheme' => 'http',
+            'dkim_key_size' => '1024'
         ]);
         $this->setHydrateClass(CreateResponse::class);
 
@@ -147,6 +151,7 @@ JSON
             'spam_action' => 'bar',
             'wildcard' => 'true',
             'web_scheme' => 'http',
+            'dkim_key_size' => '1024'
         ]);
         $this->setHydrateClass(CreateResponse::class);
 
@@ -163,6 +168,7 @@ JSON
             'smtp_password' => 'foo',
             'force_dkim_authority' => 'true',
             'web_scheme' => 'http',
+            'dkim_key_size' => '1024'
         ]);
         $this->setHydrateClass(CreateResponse::class);
 
@@ -181,6 +187,7 @@ JSON
             'wildcard' => 'true',
             'force_dkim_authority' => 'true',
             'web_scheme' => 'http',
+            'dkim_key_size' => '1024'
         ]);
         $this->setHydrateClass(CreateResponse::class);
 
@@ -278,6 +285,7 @@ JSON
             'smtp_password' => 'foo',
             'ips' => '127.0.0.1,127.0.0.2',
             'web_scheme' => 'http',
+            'dkim_key_size' => '1024'
         ]);
         $this->setHydrateClass(CreateResponse::class);
 
@@ -285,6 +293,22 @@ JSON
         $api->create('example.com', 'foo', null, null, null, ['127.0.0.1', '127.0.0.2']);
     }
 
+    public function testCreateWithDkim()
+    {
+        $this->setRequestMethod('POST');
+        $this->setRequestUri('/v3/domains');
+        $this->setRequestBody([
+            'name' => 'example.com',
+            'smtp_password' => 'foo',
+            'web_scheme' => 'http',
+            'dkim_key_size' => '2048'
+        ]);
+        $this->setHydrateClass(CreateResponse::class);
+
+        $api = $this->getApiInstance();
+        $api->create('example.com', 'foo', null, null, null, null, null, 'http', '2048');
+    }
+
     public function testCreateWithWebSchema()
     {
         $this->setRequestMethod('POST');
@@ -293,6 +317,7 @@ JSON
             'name' => 'example.com',
             'smtp_password' => 'foo',
             'web_scheme' => 'https',
+            'dkim_key_size' => '1024'
         ]);
         $this->setHydrateClass(CreateResponse::class);