diff --git a/src/Seld/JsonLint/JsonParser.php b/src/Seld/JsonLint/JsonParser.php
index 575011f..41c36ec 100644
--- a/src/Seld/JsonLint/JsonParser.php
+++ b/src/Seld/JsonLint/JsonParser.php
@@ -198,9 +198,9 @@ public function parse($input, $flags = 0)
                     }
 
                     $message = null;
-                    if (\in_array("'STRING'", $expected) && \in_array(substr($this->lexer->match, 0, 1), array('"', "'"))) {
+                    if (\in_array("'STRING'", $expected) && \in_array(mb_substr($this->lexer->match, 0, 1), array('"', "'"))) {
                         $message = "Invalid string";
-                        if ("'" === substr($this->lexer->match, 0, 1)) {
+                        if ("'" === mb_substr($this->lexer->match, 0, 1)) {
                             $message .= ", it appears you used single quotes instead of double quotes";
                         } elseif (preg_match('{".+?(\\\\[^"bfnrt/\\\\u](...)?)}', $this->lexer->getFullUpcomingInput(), $match)) {
                             $message .= ", it appears you have an unescaped backslash at: ".$match[1];
@@ -218,7 +218,7 @@ public function parse($input, $flags = 0)
                         $errStr .= implode(', ', $expected);
                     }
 
-                    if (',' === substr(trim($this->lexer->getPastInput()), -1)) {
+                    if (',' === mb_substr(trim($this->lexer->getPastInput()), -1)) {
                         $errStr .= " - It appears you have an extra trailing comma";
                     }
 
@@ -347,10 +347,10 @@ private function performAction(stdClass $yyval, $yytext, $yyleng, $yylineno, $yy
             $yyval->token = $yytext;
             break;
         case 2:
-            if (strpos($yytext, 'e') !== false || strpos($yytext, 'E') !== false) {
+            if (mb_strpos($yytext, 'e') !== false || mb_strpos($yytext, 'E') !== false) {
                 $yyval->token = \floatval($yytext);
             } else {
-                $yyval->token = strpos($yytext, '.') === false ? \intval($yytext) : \floatval($yytext);
+                $yyval->token = mb_strpos($yytext, '.') === false ? \intval($yytext) : \floatval($yytext);
             }
             break;
         case 3:
@@ -468,7 +468,7 @@ private function stringInterpolation($match)
         case '\/':
             return "/";
         default:
-            return html_entity_decode('&#x'.ltrim(substr($match[0], 2), '0').';', ENT_QUOTES, 'UTF-8');
+            return html_entity_decode('&#x'.ltrim(mb_substr($match[0], 2), '0').';', ENT_QUOTES, 'UTF-8');
         }
     }
 
@@ -495,7 +495,7 @@ private function failOnBOM($input)
         // UTF-8 ByteOrderMark sequence
         $bom = "\xEF\xBB\xBF";
 
-        if (substr($input, 0, 3) === $bom) {
+        if (mb_substr($input, 0, 3) === $bom) {
             $this->parseError("BOM detected, make sure your input does not include a Unicode Byte-Order-Mark", array());
         }
     }
diff --git a/src/Seld/JsonLint/Lexer.php b/src/Seld/JsonLint/Lexer.php
index 868ee34..a782844 100644
--- a/src/Seld/JsonLint/Lexer.php
+++ b/src/Seld/JsonLint/Lexer.php
@@ -20,20 +20,20 @@ class Lexer
 {
     private $EOF = 1;
     private $rules = array(
-        0 => '/\G\s+/',
-        1 => '/\G-?([0-9]|[1-9][0-9]+)(\.[0-9]+)?([eE][+-]?[0-9]+)?\b/',
-        2 => '{\G"(?>\\\\["bfnrt/\\\\]|\\\\u[a-fA-F0-9]{4}|[^\0-\x1f\\\\"]++)*+"}',
-        3 => '/\G\{/',
-        4 => '/\G\}/',
-        5 => '/\G\[/',
-        6 => '/\G\]/',
-        7 => '/\G,/',
-        8 => '/\G:/',
-        9 => '/\Gtrue\b/',
-        10 => '/\Gfalse\b/',
-        11 => '/\Gnull\b/',
-        12 => '/\G$/',
-        13 => '/\G./',
+        0 => '/\G\s+/u',
+        1 => '/\G-?([0-9]|[1-9][0-9]+)(\.[0-9]+)?([eE][+-]?[0-9]+)?\b/u',
+        2 => '{\G"(?>\\\\["bfnrt/\\\\]|\\\\u[a-fA-F0-9]{4}|[^\0-\x1f\\\\"]++)*+"}u',
+        3 => '/\G\{/u',
+        4 => '/\G\}/u',
+        5 => '/\G\[/u',
+        6 => '/\G\]/u',
+        7 => '/\G,/u',
+        8 => '/\G:/u',
+        9 => '/\Gtrue\b/u',
+        10 => '/\Gfalse\b/u',
+        11 => '/\Gnull\b/u',
+        12 => '/\G$/u',
+        13 => '/\G./u',
     );
 
     private $conditions = array(
@@ -82,37 +82,37 @@ public function setInput($input)
     public function showPosition()
     {
         $pre = str_replace("\n", '', $this->getPastInput());
-        $c = str_repeat('-', max(0, \strlen($pre) - 1)); // new Array(pre.length + 1).join("-");
+        $c = str_repeat('-', max(0, \mb_strlen($pre) - 1)); // new Array(pre.length + 1).join("-");
 
         return $pre . str_replace("\n", '', $this->getUpcomingInput()) . "\n" . $c . "^";
     }
 
     public function getPastInput()
     {
-        $pastLength = $this->offset - \strlen($this->match);
+        $pastLength = $this->offset - \mb_strlen($this->match);
 
-        return ($pastLength > 20 ? '...' : '') . substr($this->input, max(0, $pastLength - 20), min(20, $pastLength));
+        return ($pastLength > 20 ? '...' : '') . mb_substr($this->input, max(0, $pastLength - 20), min(20, $pastLength));
     }
 
     public function getUpcomingInput()
     {
         $next = $this->match;
-        if (\strlen($next) < 20) {
-            $next .= substr($this->input, $this->offset, 20 - \strlen($next));
+        if (\mb_strlen($next) < 20) {
+            $next .= mb_substr($this->input, $this->offset, 20 - \mb_strlen($next));
         }
 
-        return substr($next, 0, 20) . (\strlen($next) > 20 ? '...' : '');
+        return mb_substr($next, 0, 20) . (\mb_strlen($next) > 20 ? '...' : '');
     }
 
     public function getFullUpcomingInput()
     {
         $next = $this->match;
-        if (substr($next, 0, 1) === '"' && substr_count($next, '"') === 1) {
-            $len = \strlen($this->input);
-            $strEnd = min(strpos($this->input, '"', $this->offset + 1) ?: $len, strpos($this->input, "\n", $this->offset + 1) ?: $len);
-            $next .= substr($this->input, $this->offset, $strEnd - $this->offset);
-        } elseif (\strlen($next) < 20) {
-            $next .= substr($this->input, $this->offset, 20 - \strlen($next));
+        if (mb_substr($next, 0, 1) === '"' && mb_substr_count($next, '"') === 1) {
+            $len = \mb_strlen($this->input);
+            $strEnd = min(mb_strpos($this->input, '"', $this->offset + 1) ?: $len, mb_strpos($this->input, "\n", $this->offset + 1) ?: $len);
+            $next .= mb_substr($this->input, $this->offset, $strEnd - $this->offset);
+        } elseif (\mb_strlen($next) < 20) {
+            $next .= mb_substr($this->input, $this->offset, 20 - \mb_strlen($next));
         }
 
         return $next;
@@ -128,7 +128,7 @@ private function next()
         if ($this->done) {
             return $this->EOF;
         }
-        if ($this->offset === \strlen($this->input)) {
+        if ($this->offset === \mb_strlen($this->input)) {
             $this->done = true;
         }
 
@@ -146,8 +146,8 @@ private function next()
         $rulesLen = \count($rules);
 
         for ($i=0; $i < $rulesLen; $i++) {
-            if (preg_match($this->rules[$rules[$i]], $this->input, $match, 0, $this->offset)) {
-                preg_match_all('/\n.*/', $match[0], $lines);
+            if (preg_match($this->rules[$rules[$i]], $this->input, $match, 0, strlen(mb_substr($this->input, 0, $this->offset)))) {
+                preg_match_all('/\n.*/u', $match[0], $lines);
                 $lines = $lines[0];
                 if ($lines) {
                     $this->yylineno += \count($lines);
@@ -157,13 +157,13 @@ private function next()
                     'first_line' => $this->yylloc['last_line'],
                     'last_line' => $this->yylineno+1,
                     'first_column' => $this->yylloc['last_column'],
-                    'last_column' => $lines ? \strlen($lines[\count($lines) - 1]) - 1 : $this->yylloc['last_column'] + \strlen($match[0]),
+                    'last_column' => $lines ? \mb_strlen($lines[\count($lines) - 1]) - 1 : $this->yylloc['last_column'] + \mb_strlen($match[0]),
                 );
                 $this->yytext .= $match[0];
                 $this->match .= $match[0];
-                $this->yyleng = \strlen($this->yytext);
+                $this->yyleng = \mb_strlen($this->yytext);
                 $this->more = false;
-                $this->offset += \strlen($match[0]);
+                $this->offset += \mb_strlen($match[0]);
                 $token = $this->performAction($rules[$i], $this->conditionStack[\count($this->conditionStack)-1]);
                 if ($token) {
                     return $token;
@@ -173,7 +173,7 @@ private function next()
             }
         }
 
-        if ($this->offset === \strlen($this->input)) {
+        if ($this->offset === \mb_strlen($this->input)) {
             return $this->EOF;
         }
 
@@ -201,7 +201,7 @@ private function performAction($avoiding_name_collisions, $YY_START)
             return 6;
            break;
         case 2:
-            $this->yytext = substr($this->yytext, 1, $this->yyleng-2);
+            $this->yytext = mb_substr($this->yytext, 1, $this->yyleng-2);
 
             return 4;
         case 3: