diff --git a/composer.json b/composer.json
index c13fd59..d6cdeef 100644
--- a/composer.json
+++ b/composer.json
@@ -18,6 +18,7 @@
         "php-mock/php-mock-phpunit": "^2.1"
     },
     "autoload": {
+        "files": ["src/string_functions.php"],
         "psr-4": {
             "TheIconic\\NameParser\\": ["src/", "tests/"]
         }
diff --git a/src/Mapper/InitialMapper.php b/src/Mapper/InitialMapper.php
index 3a75dc4..48bcddf 100644
--- a/src/Mapper/InitialMapper.php
+++ b/src/Mapper/InitialMapper.php
@@ -4,6 +4,8 @@
 
 use TheIconic\NameParser\Part\AbstractPart;
 use TheIconic\NameParser\Part\Initial;
+use function TheIconic\NameParser\characters;
+use function TheIconic\NameParser\strlen;
 
 /**
  * single letter, possibly followed by a period
@@ -46,7 +48,7 @@ public function map(array $parts): array
                 $length = strlen($stripped);
 
                 if (1 < $length && $length <= $this->combinedMax) {
-                    array_splice($parts, $k, 1, str_split($stripped));
+                    array_splice($parts, $k, 1, characters($stripped));
                     $last = count($parts) - 1;
                     $part = $parts[$k];
                 }
diff --git a/src/Mapper/LastnameMapper.php b/src/Mapper/LastnameMapper.php
index 43cfdc7..67fbae9 100644
--- a/src/Mapper/LastnameMapper.php
+++ b/src/Mapper/LastnameMapper.php
@@ -2,13 +2,13 @@
 
 namespace TheIconic\NameParser\Mapper;
 
-use TheIconic\NameParser\LanguageInterface;
 use TheIconic\NameParser\Part\AbstractPart;
 use TheIconic\NameParser\Part\Lastname;
 use TheIconic\NameParser\Part\LastnamePrefix;
 use TheIconic\NameParser\Part\Nickname;
 use TheIconic\NameParser\Part\Salutation;
 use TheIconic\NameParser\Part\Suffix;
+use function TheIconic\NameParser\strlen;
 
 class LastnameMapper extends AbstractMapper
 {
diff --git a/src/Part/AbstractPart.php b/src/Part/AbstractPart.php
index 51e6372..cb9a5a2 100644
--- a/src/Part/AbstractPart.php
+++ b/src/Part/AbstractPart.php
@@ -2,6 +2,8 @@
 
 namespace TheIconic\NameParser\Part;
 
+use function TheIconic\NameParser\tcword;
+
 abstract class AbstractPart
 {
     /**
@@ -81,10 +83,6 @@ protected function camelcase($word): string
      */
     protected function camelcaseReplace($matches): string
     {
-        if (function_exists('mb_convert_case')) {
-            return mb_convert_case($matches[0], MB_CASE_TITLE, 'UTF-8');
-        }
-        
-        return ucfirst(strtolower($matches[0]));
+        return tcword($matches[0]);
     }
 }
diff --git a/src/string_functions.php b/src/string_functions.php
new file mode 100644
index 0000000..7f869ab
--- /dev/null
+++ b/src/string_functions.php
@@ -0,0 +1,9 @@
+<?php
+
+if (!function_exists('TheIconic\NameParser\strlen')) {
+    if (extension_loaded('mbstring')) {
+        require __DIR__ . '/string_functions_mbstring.php';
+    } else {
+        require __DIR__ . '/string_functions_native.php';
+    }
+}
diff --git a/src/string_functions_mbstring.php b/src/string_functions_mbstring.php
new file mode 100644
index 0000000..8cc8f21
--- /dev/null
+++ b/src/string_functions_mbstring.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace TheIconic\NameParser;
+
+if (!function_exists('TheIconic\NameParser\strlen')) {
+    function strlen(string $string): int
+    {
+        return \mb_strlen($string, 'UTF-8');
+    }
+}
+
+if (!function_exists('TheIconic\NameParser\tcword')) {
+    function tcword(string $string): string
+    {
+        return \mb_convert_case($string, MB_CASE_TITLE, 'UTF-8');
+    }
+}
+
+if (!function_exists('TheIconic\NameParser\characters')) {
+    function characters(string $string): array
+    {
+        return $charactersAsArray = \preg_split('//u', $string, null, PREG_SPLIT_NO_EMPTY);
+    }
+}
+
+if (!function_exists('TheIconic\NameParser\substr')) {
+    function substr(string $string, int $start, int $length = null): string
+    {
+        return \mb_substr($string, $start, $length, 'UTF-8');
+    }
+}
diff --git a/src/string_functions_native.php b/src/string_functions_native.php
new file mode 100644
index 0000000..84220ba
--- /dev/null
+++ b/src/string_functions_native.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace TheIconic\NameParser;
+
+if (!function_exists('TheIconic\NameParser\strlen')) {
+    function strlen(string $string): int
+    {
+        return \strlen($string);
+    }
+}
+
+if (!function_exists('TheIconic\NameParser\tcword')) {
+    function tcword(string $string): string
+    {
+        return \ucfirst(\strtolower($string));
+    }
+}
+
+if (!function_exists('TheIconic\NameParser\characters')) {
+    function characters(string $string): array
+    {
+        return \str_split($string, $split_length = 1);
+    }
+}
+
+if (!function_exists('TheIconic\NameParser\substr')) {
+    function substr(string $string, int $start, int $length = null): string
+    {
+        return \substr($string, $start, $length);
+    }
+}