diff --git a/CHANGELOG.md b/CHANGELOG.md
index a8abd6a..c74d963 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+6.7.1
+-----
+
+* `LtiMessage` auto submit script wrapped by `window.onload` callback
+
 6.7.0
 -----
 
diff --git a/src/Message/LtiMessage.php b/src/Message/LtiMessage.php
index 1eff7d6..6d7aff7 100644
--- a/src/Message/LtiMessage.php
+++ b/src/Message/LtiMessage.php
@@ -105,7 +105,10 @@ public function toHtmlRedirectForm(bool $autoSubmit = true): string
             $formInputs[] = sprintf('<input type="hidden" name="%s" value="%s"/>', $name, $value);
         }
 
-        $autoSubmitScript = sprintf('<script>document.getElementById("%s").submit();</script>', $formId);
+        $autoSubmitScript = sprintf(
+            '<script>window.onload=function(){document.getElementById("%s").submit()}</script>',
+            $formId
+        );
 
         return sprintf(
             '<form id="%s" action="%s" method="POST">%s</form>%s',
diff --git a/tests/Unit/Message/LtiMessageTest.php b/tests/Unit/Message/LtiMessageTest.php
index 4c50cad..6eb179a 100644
--- a/tests/Unit/Message/LtiMessageTest.php
+++ b/tests/Unit/Message/LtiMessageTest.php
@@ -143,7 +143,7 @@ public function testToHtmlLink(): void
     public function testToHtmlRedirectForm(): void
     {
         $this->assertEquals(
-            '<form id="launch_0e7d4b4c23fd7b077aba0602246820ff" action="http://example.com" method="POST"><input type="hidden" name="parameter" value="value"/></form><script>document.getElementById("launch_0e7d4b4c23fd7b077aba0602246820ff").submit();</script>',
+            '<form id="launch_0e7d4b4c23fd7b077aba0602246820ff" action="http://example.com" method="POST"><input type="hidden" name="parameter" value="value"/></form><script>window.onload=function(){document.getElementById("launch_0e7d4b4c23fd7b077aba0602246820ff").submit()}</script>',
             $this->subject->toHtmlRedirectForm()
         );
     }
diff --git a/tests/Unit/Security/Oidc/Server/OidcAuthenticationRequestHandlerTest.php b/tests/Unit/Security/Oidc/Server/OidcAuthenticationRequestHandlerTest.php
index a866863..6871bc1 100644
--- a/tests/Unit/Security/Oidc/Server/OidcAuthenticationRequestHandlerTest.php
+++ b/tests/Unit/Security/Oidc/Server/OidcAuthenticationRequestHandlerTest.php
@@ -65,7 +65,7 @@ public function testAuthenticationSuccessResponse(): void
 
         $this->assertEquals(200, $response->getStatusCode());
         $this->assertEquals(
-            '<form id="launch_0e7d4b4c23fd7b077aba0602246820ff" action="http://example.com" method="POST"><input type="hidden" name="parameter" value="value"/></form><script>document.getElementById("launch_0e7d4b4c23fd7b077aba0602246820ff").submit();</script>',
+            '<form id="launch_0e7d4b4c23fd7b077aba0602246820ff" action="http://example.com" method="POST"><input type="hidden" name="parameter" value="value"/></form><script>window.onload=function(){document.getElementById("launch_0e7d4b4c23fd7b077aba0602246820ff").submit()}</script>',
             (string)$response->getBody()
         );
     }