diff --git a/src/Faker/Guesser/Name.php b/src/Faker/Guesser/Name.php
index 39f2a065..6552e32d 100644
--- a/src/Faker/Guesser/Name.php
+++ b/src/Faker/Guesser/Name.php
@@ -13,7 +13,7 @@ class Name
 
 	public function guessFormat($name)
 	{
-		$name = strtolower($name);
+		$name = static::toLower($name);
 		$generator = $this->generator;
 		if (preg_match('/^is[_A-Z]/', $name)) {
 			return function() use ($generator) { return $generator->boolean; };
diff --git a/src/Faker/ORM/Propel/EntityPopulator.php b/src/Faker/ORM/Propel/EntityPopulator.php
index 20df3fae..0dd2f59d 100644
--- a/src/Faker/ORM/Propel/EntityPopulator.php
+++ b/src/Faker/ORM/Propel/EntityPopulator.php
@@ -77,7 +77,7 @@ class EntityPopulator
 	protected function isColumnBehavior($columnMap)
 	{
 		foreach ($columnMap->getTable()->getBehaviors() as $name => $params) {
-			$columnName = strtolower($columnMap->getName());
+			$columnName = static::toLower($columnMap->getName());
 			switch ($name) {
 				case 'nested_set':
 					$columnNames = array($params['left_column'], $params['right_column'], $params['level_column']);
diff --git a/src/Faker/Provider/Address.php b/src/Faker/Provider/Address.php
index 68488fce..49a382cb 100644
--- a/src/Faker/Provider/Address.php
+++ b/src/Faker/Provider/Address.php
@@ -79,7 +79,7 @@ class Address extends \Faker\Provider\Base
 	 */
 	public static function postcode()
 	{
-		return strtoupper(static::bothify(static::randomElement(static::$postcode)));
+		return static::toUpper(static::bothify(static::randomElement(static::$postcode)));
 	}
 
 	/**
diff --git a/src/Faker/Provider/Base.php b/src/Faker/Provider/Base.php
index 74526059..4430e618 100644
--- a/src/Faker/Provider/Base.php
+++ b/src/Faker/Provider/Base.php
@@ -126,4 +126,24 @@ class Base
 	{
 		return static::lexify(static::numerify($string));
 	}
-}
\ No newline at end of file
+
+	/**
+	 * Converts string to lowercase.
+	 * Uses mb_string extension if available
+	 * @param string $string String that should be converted to lowercase
+	 * @return string
+	 */
+	public static function toLower($string) {
+		return extension_loaded('mbstring') ? mb_strtolower($string) : strtolower($string);
+	}
+
+	/**
+	 * Converts string to uppercase.
+	 * Uses mb_string extension if available
+	 * @param string $string String that should be converted to uppercase
+	 * @return string
+	 */
+	public static function toUpper($string) {
+		return extension_loaded('mbstring') ? mb_strtoupper($string) : strtoupper($string);
+	}
+}
diff --git a/src/Faker/Provider/Internet.php b/src/Faker/Provider/Internet.php
index 08a5293c..7f8284ed 100644
--- a/src/Faker/Provider/Internet.php
+++ b/src/Faker/Provider/Internet.php
@@ -70,7 +70,7 @@ class Internet extends \Faker\Provider\Base
 	public function userName()
 	{
 		$format = static::randomElement(static::$userNameFormats);
-		return strtolower(static::bothify($this->generator->parse($format)));
+		return static::toLower(static::bothify($this->generator->parse($format)));
 	}
 
 	/**
@@ -91,7 +91,7 @@ class Internet extends \Faker\Provider\Base
 		$company = $companyElements[0];
 		$company = preg_replace('/\W/', '', $company);
 
-		return strtolower($company);
+		return static::toLower($company);
 	}
 
 	/**
diff --git a/src/Faker/Provider/Lorem.php b/src/Faker/Provider/Lorem.php
index 5cc599bc..db67189e 100644
--- a/src/Faker/Provider/Lorem.php
+++ b/src/Faker/Provider/Lorem.php
@@ -74,7 +74,7 @@ class Lorem extends \Faker\Provider\Base
 	 *
  	 * @example 'Lorem ipsum dolor sit amet.'
 	 * @param integer $nbWords around how many words the sentence should contain
-	 * @param boolean $variableNbWords set to false if you want exactly $nbWords returned, 
+	 * @param boolean $variableNbWords set to false if you want exactly $nbWords returned,
 	 *                                 otherwise $nbWords may vary by +/-40% with a minimum of 1
 	 * @return string
 	 */
@@ -115,7 +115,7 @@ class Lorem extends \Faker\Provider\Base
 	 *
  	 * @example 'Sapiente sunt omnis. Ut pariatur ad autem ducimus et. Voluptas rem voluptas sint modi dolorem amet.'
 	 * @param integer $nbSentences around how many sentences the paragraph should contain
-	 * @param boolean $variableNbSentences set to false if you want exactly $nbSentences returned, 
+	 * @param boolean $variableNbSentences set to false if you want exactly $nbSentences returned,
 	 *                                     otherwise $nbSentences may vary by +/-40% with a minimum of 1
 	 * @return string
 	 */
@@ -173,7 +173,7 @@ class Lorem extends \Faker\Provider\Base
 				}
 				array_pop($text);
 			}
-			$text[0][0] = strtoupper($text[0][0]);
+			$text[0][0] = static::toUpper($text[0][0]);
 			$text[count($text) - 1] .= '.';
 		} else if ($maxNbChars < 100) {
 			// join sentences
diff --git a/src/Faker/Provider/da_DK/Address.php b/src/Faker/Provider/da_DK/Address.php
index 1742875b..9f0f3782 100644
--- a/src/Faker/Provider/da_DK/Address.php
+++ b/src/Faker/Provider/da_DK/Address.php
@@ -235,9 +235,14 @@ class Address extends \Faker\Provider\Address
         return static::randomElement(static::$streetSuffixWord);
     }
 
+    /**
+     * Randomly return a building number.
+     *
+     * @return string
+     */
     public static function buildingNumber()
     {
-        return strtoupper(static::bothify(static::randomElement(static::$buildingNumber)));
+        return static::toUpper(static::bothify(static::randomElement(static::$buildingNumber)));
     }
 
     /**
diff --git a/src/Faker/Provider/da_DK/Internet.php b/src/Faker/Provider/da_DK/Internet.php
index 4052a758..f851871e 100644
--- a/src/Faker/Provider/da_DK/Internet.php
+++ b/src/Faker/Provider/da_DK/Internet.php
@@ -48,7 +48,7 @@ class Internet extends \Faker\Provider\Internet
     public function userName()
     {
         $format = static::randomElement(static::$userNameFormats);
-        return strtolower(static::toAscii(static::bothify($this->generator->parse($format))));
+        return static::toLower(static::toAscii(static::bothify($this->generator->parse($format))));
     }
 
     /**
@@ -62,6 +62,6 @@ class Internet extends \Faker\Provider\Internet
         $company = $companyElements[0];
         $company = preg_replace('/\W/', '', $company);
 
-        return strtolower(static::toAscii($company));
+        return static::toLower(static::toAscii($company));
     }
 }
diff --git a/src/Faker/Provider/de_DE/Internet.php b/src/Faker/Provider/de_DE/Internet.php
index 70d7d033..c3f0349a 100644
--- a/src/Faker/Provider/de_DE/Internet.php
+++ b/src/Faker/Provider/de_DE/Internet.php
@@ -27,7 +27,7 @@ class Internet extends \Faker\Provider\Internet
 	public function userName()
 	{
 		$format = static::randomElement(static::$userNameFormats);
-		return strtolower(static::toAscii(static::bothify($this->generator->parse($format))));
+		return static::toLower(static::toAscii(static::bothify($this->generator->parse($format))));
 	}
 
 	/**
@@ -40,6 +40,6 @@ class Internet extends \Faker\Provider\Internet
 		$company = $companyElements[0];
 		$company = preg_replace('/\W/', '', $company);
 
-		return strtolower(static::toAscii($company));
+		return static::toLower(static::toAscii($company));
 	}
 }
diff --git a/src/Faker/Provider/fr_FR/Internet.php b/src/Faker/Provider/fr_FR/Internet.php
index f26529d6..d5c69c91 100644
--- a/src/Faker/Provider/fr_FR/Internet.php
+++ b/src/Faker/Provider/fr_FR/Internet.php
@@ -27,7 +27,7 @@ class Internet extends \Faker\Provider\Internet
 	public function userName()
 	{
 		$format = static::randomElement(static::$userNameFormats);
-		return strtolower(static::toAscii(static::bothify($this->generator->parse($format))));
+		return static::toLower(static::toAscii(static::bothify($this->generator->parse($format))));
 	}
 
 	/**
@@ -40,6 +40,6 @@ class Internet extends \Faker\Provider\Internet
 		$company = $companyElements[0];
 		$company = preg_replace('/\W/', '', $company);
 
-		return strtolower(static::toAscii($company));
+		return static::toLower(static::toAscii($company));
 	}
 }
diff --git a/src/Faker/Provider/ru_RU/Address.php b/src/Faker/Provider/ru_RU/Address.php
index 97d9351b..23116e31 100644
--- a/src/Faker/Provider/ru_RU/Address.php
+++ b/src/Faker/Provider/ru_RU/Address.php
@@ -115,7 +115,7 @@ class Address extends \Faker\Provider\Base
 
 	public static function postcode()
 	{
-		return strtoupper(static::bothify(static::randomElement(static::$postcode)));
+		return static::toUpper(static::bothify(static::randomElement(static::$postcode)));
 	}
 
 	public static function regionSuffix()