diff --git a/src/Plugin/Block/SuperfishBlock.php b/src/Plugin/Block/SuperfishBlock.php
index 15b3ad2..ea79feb 100644
--- a/src/Plugin/Block/SuperfishBlock.php
+++ b/src/Plugin/Block/SuperfishBlock.php
@@ -1253,7 +1253,7 @@ class SuperfishBlock extends SystemMenuBlock {
 
                 case 1:
                   $sfplugins['touchscreen']['mode'] = 'useragent_custom';
-                  $tsual = drupal_strtolower($this->configuration['touchual']);
+                  $tsual = mb_strtolower($this->configuration['touchual']);
                   if (strpos($tsual, '*')) {
                     $tsual = str_replace('*', '|', $tsual);
                   }
@@ -1266,7 +1266,7 @@ class SuperfishBlock extends SystemMenuBlock {
             // Server-side.
             case 1:
               if (isset($_SERVER['HTTP_USER_AGENT'])) {
-                $hua = drupal_strtolower($_SERVER['HTTP_USER_AGENT']);
+                $hua = mb_strtolower($_SERVER['HTTP_USER_AGENT']);
                 switch ($tsua) {
                   // Use the pre-defined list of mobile UA strings.
                   case 0:
@@ -1280,7 +1280,7 @@ class SuperfishBlock extends SystemMenuBlock {
 
                   // Use the custom list of UA strings.
                   case 1:
-                    $tsual = drupal_strtolower($this->configuration['touchual']);
+                    $tsual = mb_strtolower($this->configuration['touchual']);
                     $tsuac = [];
                     if (strpos($tsual, '*')) {
                       $tsual = explode('*', $tsual);
@@ -1342,7 +1342,7 @@ class SuperfishBlock extends SystemMenuBlock {
 
                 case 1:
                   $sfplugins['smallscreen']['mode'] = 'useragent_custom';
-                  $ssual = drupal_strtolower($this->configuration['smallual']);
+                  $ssual = mb_strtolower($this->configuration['smallual']);
                   if (strpos($ssual, '*')) {
                     $ssual = str_replace('*', '|', $ssual);
                   }
@@ -1355,7 +1355,7 @@ class SuperfishBlock extends SystemMenuBlock {
             // Server-side.
             case 1:
               if (isset($_SERVER['HTTP_USER_AGENT'])) {
-                $hua = drupal_strtolower($_SERVER['HTTP_USER_AGENT']);
+                $hua = mb_strtolower($_SERVER['HTTP_USER_AGENT']);
                 switch ($ssua) {
                   // Use the pre-defined list of mobile UA strings.
                   case 0:
@@ -1367,7 +1367,7 @@ class SuperfishBlock extends SystemMenuBlock {
                   // Use the custom list of UA strings.
                   case 1:
                     $ssual = $this->configuration['smallual'];
-                    $ssual = drupal_strtolower($ssual);
+                    $ssual = mb_strtolower($ssual);
                     $ssuac = [];
                     if (strpos($ssual, '*')) {
                       $ssual = explode('*', $ssual);