diff --git a/src/ExpressionParser.php b/src/ExpressionParser.php
index d09cfbb48..d45860840 100644
--- a/src/ExpressionParser.php
+++ b/src/ExpressionParser.php
@@ -707,7 +707,7 @@ class ExpressionParser
                 $stream->expect(Token::NAME_TYPE, null, 'Only variables can be assigned to');
             }
             $value = $token->getValue();
-            if (\in_array(strtr($value, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'), ['true', 'false', 'none', 'null'])) {
+            if (\in_array(strtolower($value), ['true', 'false', 'none', 'null'])) {
                 throw new SyntaxError(\sprintf('You cannot assign a value to "%s".', $value), $token->getLine(), $stream->getSourceContext());
             }
             $targets[] = new AssignNameExpression($value, $token->getLine());
diff --git a/src/Extension/CoreExtension.php b/src/Extension/CoreExtension.php
index fe5ed184d..06b19d8bb 100644
--- a/src/Extension/CoreExtension.php
+++ b/src/Extension/CoreExtension.php
@@ -1686,7 +1686,7 @@ final class CoreExtension extends AbstractExtension
         if (!isset($cache[$class])) {
             $methods = get_class_methods($object);
             sort($methods);
-            $lcMethods = array_map(function ($value) { return strtr($value, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'); }, $methods);
+            $lcMethods = array_map('strtolower', $methods);
             $classCache = [];
             foreach ($methods as $i => $method) {
                 $classCache[$method] = $method;
@@ -1725,7 +1725,7 @@ final class CoreExtension extends AbstractExtension
         $call = false;
         if (isset($cache[$class][$item])) {
             $method = $cache[$class][$item];
-        } elseif (isset($cache[$class][$lcItem = strtr($item, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz')])) {
+        } elseif (isset($cache[$class][$lcItem = strtolower($item)])) {
             $method = $cache[$class][$lcItem];
         } elseif (isset($cache[$class]['__call'])) {
             $method = $item;
diff --git a/src/Sandbox/SecurityPolicy.php b/src/Sandbox/SecurityPolicy.php
index 988e37216..b0d054260 100644
--- a/src/Sandbox/SecurityPolicy.php
+++ b/src/Sandbox/SecurityPolicy.php
@@ -50,7 +50,7 @@ final class SecurityPolicy implements SecurityPolicyInterface
     {
         $this->allowedMethods = [];
         foreach ($methods as $class => $m) {
-            $this->allowedMethods[$class] = array_map(function ($value) { return strtr($value, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'); }, \is_array($m) ? $m : [$m]);
+            $this->allowedMethods[$class] = array_map('strtolower', \is_array($m) ? $m : [$m]);
         }
     }
 
@@ -98,7 +98,7 @@ final class SecurityPolicy implements SecurityPolicyInterface
         }
 
         $allowed = false;
-        $method = strtr($method, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz');
+        $method = strtolower($method);
         foreach ($this->allowedMethods as $class => $methods) {
             if ($obj instanceof $class && \in_array($method, $methods)) {
                 $allowed = true;