diff --git a/src/Symfony/Component/Form/Extension/Core/DataTransformer/NumberToLocalizedStringTransformer.php b/src/Symfony/Component/Form/Extension/Core/DataTransformer/NumberToLocalizedStringTransformer.php
index b5cdae110d5a..7c21249fad5b 100644
--- a/src/Symfony/Component/Form/Extension/Core/DataTransformer/NumberToLocalizedStringTransformer.php
+++ b/src/Symfony/Component/Form/Extension/Core/DataTransformer/NumberToLocalizedStringTransformer.php
@@ -80,6 +80,9 @@ public function transform($value)
             throw new TransformationFailedException($formatter->getErrorMessage());
         }
 
+        // Convert fixed spaces to normal ones
+        $value = str_replace("\xc2\xa0", ' ', $value);
+
         return $value;
     }
 
@@ -130,19 +133,31 @@ public function reverseTransform($value)
             throw new TransformationFailedException('I don\'t have a clear idea what infinity looks like');
         }
 
+        if (function_exists('mb_detect_encoding') && false !== $encoding = mb_detect_encoding($value)) {
+            $strlen = function ($string) use ($encoding) {
+                return mb_strlen($string, $encoding);
+            };
+            $substr = function ($string, $offset, $length) use ($encoding) {
+                return mb_substr($string, $offset, $length, $encoding);
+            };
+        } else {
+            $strlen = 'strlen';
+            $substr = 'substr';
+        }
+
+        $length = $strlen($value);
+
         // After parsing, position holds the index of the character where the
         // parsing stopped
-        if ($position < strlen($value)) {
+        if ($position < $length) {
             // Check if there are unrecognized characters at the end of the
-            // number
-            $remainder = substr($value, $position);
+            // number (excluding whitespace characters)
+            $remainder = trim($substr($value, $position, $length), " \t\n\r\0\x0b\xc2\xa0");
 
-            // Remove all whitespace characters
-            if ('' !== preg_replace('/[\s\xc2\xa0]*/', '', $remainder)) {
+            if ('' !== $remainder) {
                 throw new TransformationFailedException(
-                    sprintf('The number contains unrecognized characters: "%s"',
-                        $remainder
-                    ));
+                    sprintf('The number contains unrecognized characters: "%s"', $remainder)
+                );
             }
         }
 
diff --git a/src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/NumberToLocalizedStringTransformerTest.php b/src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/NumberToLocalizedStringTransformerTest.php
index 151dbc80f606..09af7243d66d 100644
--- a/src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/NumberToLocalizedStringTransformerTest.php
+++ b/src/Symfony/Component/Form/Tests/Extension/Core/DataTransformer/NumberToLocalizedStringTransformerTest.php
@@ -22,29 +22,52 @@ protected function setUp()
         \Locale::setDefault('de_AT');
     }
 
-    public function testTransform()
+    public function provideTransformations()
     {
-        $transformer = new NumberToLocalizedStringTransformer();
-
-        $this->assertEquals('1', $transformer->transform(1));
-        $this->assertEquals('1,5', $transformer->transform(1.5));
-        $this->assertEquals('1234,5', $transformer->transform(1234.5));
-        $this->assertEquals('12345,912', $transformer->transform(12345.9123));
+        return array(
+            array(null, '', 'de_AT'),
+            array(1, '1', 'de_AT'),
+            array(1.5, '1,5', 'de_AT'),
+            array(1234.5, '1234,5', 'de_AT'),
+            array(12345.912, '12345,912', 'de_AT'),
+            array(1234.5, '1234,5', 'ru'),
+            array(1234.5, '1234,5', 'fi'),
+        );
     }
 
-    public function testTransformEmpty()
+    /**
+     * @dataProvider provideTransformations
+     */
+    public function testTransform($from, $to, $locale)
     {
+        \Locale::setDefault($locale);
+
         $transformer = new NumberToLocalizedStringTransformer();
 
-        $this->assertSame('', $transformer->transform(null));
+        $this->assertSame($to, $transformer->transform($from));
+    }
+
+    public function provideTransformationsWithGrouping()
+    {
+        return array(
+            array(1234.5, '1.234,5', 'de_AT'),
+            array(12345.912, '12.345,912', 'de_AT'),
+            array(1234.5, '1 234,5', 'fr'),
+            array(1234.5, '1 234,5', 'ru'),
+            array(1234.5, '1 234,5', 'fi'),
+        );
     }
 
-    public function testTransformWithGrouping()
+    /**
+     * @dataProvider provideTransformationsWithGrouping
+     */
+    public function testTransformWithGrouping($from, $to, $locale)
     {
+        \Locale::setDefault($locale);
+
         $transformer = new NumberToLocalizedStringTransformer(null, true);
 
-        $this->assertEquals('1.234,5', $transformer->transform(1234.5));
-        $this->assertEquals('12.345,912', $transformer->transform(12345.9123));
+        $this->assertSame($to, $transformer->transform($from));
     }
 
     public function testTransformWithPrecision()
@@ -65,30 +88,48 @@ public function testTransformWithRoundingMode()
 
     }
 
-    public function testReverseTransform()
+    /**
+     * @dataProvider provideTransformations
+     */
+    public function testReverseTransform($to, $from, $locale)
     {
+        \Locale::setDefault($locale);
+
         $transformer = new NumberToLocalizedStringTransformer();
 
-        $this->assertEquals(1, $transformer->reverseTransform('1'));
-        $this->assertEquals(1.5, $transformer->reverseTransform('1,5'));
-        $this->assertEquals(1234.5, $transformer->reverseTransform('1234,5'));
-        $this->assertEquals(12345.912, $transformer->reverseTransform('12345,912'));
+        $this->assertEquals($to, $transformer->reverseTransform($from));
     }
 
-    public function testReverseTransformEmpty()
+    /**
+     * @dataProvider provideTransformationsWithGrouping
+     */
+    public function testReverseTransformWithGrouping($to, $from, $locale)
     {
-        $transformer = new NumberToLocalizedStringTransformer();
+        \Locale::setDefault($locale);
+
+        $transformer = new NumberToLocalizedStringTransformer(null, true);
+
+        $this->assertEquals($to, $transformer->reverseTransform($from));
+    }
+
+    // https://github.com/symfony/symfony/issues/7609
+    public function testReverseTransformWithGroupingAndFixedSpaces()
+    {
+        if (!extension_loaded('mbstring')) {
+            $this->markTestSkipped('The "mbstring" extension is required for this test.');
+        }
+
+        \Locale::setDefault('ru');
+
+        $transformer = new NumberToLocalizedStringTransformer(null, true);
 
-        $this->assertNull($transformer->reverseTransform(''));
+        $this->assertEquals(1234.5, $transformer->reverseTransform("1\xc2\xa0234,5"));
     }
 
-    public function testReverseTransformWithGrouping()
+    public function testReverseTransformWithGroupingButWithoutGroupSeparator()
     {
         $transformer = new NumberToLocalizedStringTransformer(null, true);
 
-        // completely valid format
-        $this->assertEquals(1234.5, $transformer->reverseTransform('1.234,5'));
-        $this->assertEquals(12345.912, $transformer->reverseTransform('12.345,912'));
         // omit group separator
         $this->assertEquals(1234.5, $transformer->reverseTransform('1234,5'));
         $this->assertEquals(12345.912, $transformer->reverseTransform('12345,912'));
@@ -299,6 +340,7 @@ public function testReverseTransformDisallowsLeadingExtraCharacters()
 
     /**
      * @expectedException \Symfony\Component\Form\Exception\TransformationFailedException
+     * @expectedExceptionMessage The number contains unrecognized characters: "foo3"
      */
     public function testReverseTransformDisallowsCenteredExtraCharacters()
     {
@@ -309,6 +351,41 @@ public function testReverseTransformDisallowsCenteredExtraCharacters()
 
     /**
      * @expectedException \Symfony\Component\Form\Exception\TransformationFailedException
+     * @expectedExceptionMessage The number contains unrecognized characters: "foo8"
+     */
+    public function testReverseTransformDisallowsCenteredExtraCharactersMultibyte()
+    {
+        if (!extension_loaded('mbstring')) {
+            $this->markTestSkipped('The "mbstring" extension is required for this test.');
+        }
+
+        \Locale::setDefault('ru');
+
+        $transformer = new NumberToLocalizedStringTransformer(null, true);
+
+        $transformer->reverseTransform("12\xc2\xa0345,67foo8");
+    }
+
+    /**
+     * @expectedException \Symfony\Component\Form\Exception\TransformationFailedException
+     * @expectedExceptionMessage The number contains unrecognized characters: "foo8"
+     */
+    public function testReverseTransformIgnoresTrailingSpacesInExceptionMessage()
+    {
+        if (!extension_loaded('mbstring')) {
+            $this->markTestSkipped('The "mbstring" extension is required for this test.');
+        }
+
+        \Locale::setDefault('ru');
+
+        $transformer = new NumberToLocalizedStringTransformer(null, true);
+
+        $transformer->reverseTransform("12\xc2\xa0345,67foo8  \xc2\xa0\t");
+    }
+
+    /**
+     * @expectedException \Symfony\Component\Form\Exception\TransformationFailedException
+     * @expectedExceptionMessage The number contains unrecognized characters: "foo"
      */
     public function testReverseTransformDisallowsTrailingExtraCharacters()
     {
@@ -316,4 +393,21 @@ public function testReverseTransformDisallowsTrailingExtraCharacters()
 
         $transformer->reverseTransform('123foo');
     }
+
+    /**
+     * @expectedException \Symfony\Component\Form\Exception\TransformationFailedException
+     * @expectedExceptionMessage The number contains unrecognized characters: "foo"
+     */
+    public function testReverseTransformDisallowsTrailingExtraCharactersMultibyte()
+    {
+        if (!extension_loaded('mbstring')) {
+            $this->markTestSkipped('The "mbstring" extension is required for this test.');
+        }
+
+        \Locale::setDefault('ru');
+
+        $transformer = new NumberToLocalizedStringTransformer(null, true);
+
+        $transformer->reverseTransform("12\xc2\xa0345,678foo");
+    }
 }