diff --git a/snappymail/v/0.0.0/app/libraries/RainLoop/Service.php b/snappymail/v/0.0.0/app/libraries/RainLoop/Service.php
index ec04ffeae..02b7a08c2 100644
--- a/snappymail/v/0.0.0/app/libraries/RainLoop/Service.php
+++ b/snappymail/v/0.0.0/app/libraries/RainLoop/Service.php
@@ -215,7 +215,7 @@ class Service
 			$sContentSecurityPolicy = \preg_replace('/(img-src[^;]+)\\shttp:(\\s|;|$)/D', '$1$2', $sContentSecurityPolicy);
 		}
 		// Internet Explorer does not support 'nonce'
-		if (!\strpos($_SERVER['HTTP_USER_AGENT'], 'Trident/') && !\strpos($_SERVER['HTTP_USER_AGENT'], 'Edge/1')) {
+		if (!isset($_SERVER['HTTP_USER_AGENT']) || (!\strpos($_SERVER['HTTP_USER_AGENT'], 'Trident/') && !\strpos($_SERVER['HTTP_USER_AGENT'], 'Edge/1'))) {
 			if ($sScriptNonce) {
 				$sContentSecurityPolicy = \str_replace('script-src', "script-src 'nonce-{$sScriptNonce}'", $sContentSecurityPolicy);
 			}