diff --git a/src/CrashDump.php b/src/CrashDump.php
index bd97b3595..469b3e4b8 100644
--- a/src/CrashDump.php
+++ b/src/CrashDump.php
@@ -47,6 +47,7 @@ use function is_resource;
 use function json_encode;
 use function json_last_error_msg;
 use function max;
+use function mb_strtoupper;
 use function mkdir;
 use function ob_end_clean;
 use function ob_get_contents;
@@ -57,7 +58,6 @@ use function phpversion;
 use function preg_replace;
 use function str_split;
 use function strpos;
-use function strtoupper;
 use function substr;
 use function time;
 use function zend_version;
@@ -172,7 +172,7 @@ class CrashDump{
 					"depends" => $d->getDepend(),
 					"softDepends" => $d->getSoftDepend(),
 					"main" => $d->getMain(),
-					"load" => strtoupper($d->getOrder()->name()),
+					"load" => mb_strtoupper($d->getOrder()->name()),
 					"website" => $d->getWebsite()
 				];
 				$this->addLine($d->getName() . " " . $d->getVersion() . " by " . implode(", ", $d->getAuthors()) . " for API(s) " . implode(", ", $d->getCompatibleApis()));
diff --git a/src/MemoryManager.php b/src/MemoryManager.php
index 137bd5d95..90acbc939 100644
--- a/src/MemoryManager.php
+++ b/src/MemoryManager.php
@@ -50,6 +50,7 @@ use function is_object;
 use function is_resource;
 use function is_string;
 use function json_encode;
+use function mb_strtoupper;
 use function min;
 use function mkdir;
 use function preg_match;
@@ -58,7 +59,6 @@ use function round;
 use function spl_object_hash;
 use function sprintf;
 use function strlen;
-use function strtoupper;
 use function substr;
 use const JSON_PRETTY_PRINT;
 use const JSON_UNESCAPED_SLASHES;
@@ -131,7 +131,7 @@ class MemoryManager{
 			if($m <= 0){
 				$defaultMemory = 0;
 			}else{
-				switch(strtoupper($matches[2])){
+				switch(mb_strtoupper($matches[2])){
 					case "K":
 						$defaultMemory = $m / 1024;
 						break;
diff --git a/src/event/EventPriority.php b/src/event/EventPriority.php
index bcb914324..fc52d99c2 100644
--- a/src/event/EventPriority.php
+++ b/src/event/EventPriority.php
@@ -25,7 +25,7 @@ namespace pocketmine\event;
 
 use function constant;
 use function defined;
-use function strtoupper;
+use function mb_strtoupper;
 
 /**
  * List of event priorities
@@ -84,7 +84,7 @@ final class EventPriority{
 	 * @throws \InvalidArgumentException
 	 */
 	public static function fromString(string $name) : int{
-		$name = strtoupper($name);
+		$name = mb_strtoupper($name);
 		$const = self::class . "::" . $name;
 		if($name !== "ALL" and defined($const)){
 			return constant($const);
diff --git a/src/item/enchantment/Enchantment.php b/src/item/enchantment/Enchantment.php
index 80e791605..313a88d84 100644
--- a/src/item/enchantment/Enchantment.php
+++ b/src/item/enchantment/Enchantment.php
@@ -26,7 +26,7 @@ namespace pocketmine\item\enchantment;
 use pocketmine\event\entity\EntityDamageEvent;
 use function constant;
 use function defined;
-use function strtoupper;
+use function mb_strtoupper;
 
 /**
  * Manages enchantment type data.
@@ -233,7 +233,7 @@ class Enchantment{
 	}
 
 	public static function fromString(string $name) : ?Enchantment{
-		$const = Enchantment::class . "::" . strtoupper($name);
+		$const = Enchantment::class . "::" . mb_strtoupper($name);
 		if(defined($const)){
 			return self::get(constant($const));
 		}