diff --git a/src/Symfony/Component/Yaml/Parser.php b/src/Symfony/Component/Yaml/Parser.php
index 52cd1867efcfd..42f61af9de0a4 100644
--- a/src/Symfony/Component/Yaml/Parser.php
+++ b/src/Symfony/Component/Yaml/Parser.php
@@ -208,7 +208,7 @@ private function doParse($value, $flags)
                     $this->refs[$isRef] = end($data);
                 }
             } elseif (
-                self::preg_match('#^(?P<key>'.Inline::REGEX_QUOTED_STRING.'|(?:![^\s]++\s++)?[^ \'"\[\{!].*?) *\:(\s++(?P<value>.+))?$#u', rtrim($this->currentLine), $values)
+                self::preg_match('#^(?P<key>'.Inline::REGEX_QUOTED_STRING.'|(?:!?!php/const:)?(?:![^\s]++\s++)?[^ \'"\[\{!].*?) *\:(\s++(?P<value>.+))?$#u', rtrim($this->currentLine), $values)
                 && (false === strpos($values['key'], ' #') || in_array($values['key'][0], array('"', "'")))
             ) {
                 if ($context && 'sequence' == $context) {
@@ -221,7 +221,14 @@ private function doParse($value, $flags)
                 try {
                     Inline::$parsedLineNumber = $this->getRealCurrentLineNb();
                     $i = 0;
-                    $key = Inline::parseScalar($values['key'], 0, null, $i, !(Yaml::PARSE_KEYS_AS_STRINGS & $flags));
+                    $evaluateKey = !(Yaml::PARSE_KEYS_AS_STRINGS & $flags);
+
+                    // constants in key will be evaluated anyway
+                    if (isset($values['key'][0]) && '!' === $values['key'][0] && Yaml::PARSE_CONSTANT & $flags) {
+                        $evaluateKey = true;
+                    }
+
+                    $key = Inline::parseScalar($values['key'], 0, null, $i, $evaluateKey);
                 } catch (ParseException $e) {
                     $e->setParsedLine($this->getRealCurrentLineNb() + 1);
                     $e->setSnippet($this->currentLine);
diff --git a/src/Symfony/Component/Yaml/Tests/ParserTest.php b/src/Symfony/Component/Yaml/Tests/ParserTest.php
index c8f4a7d40e35e..a0bef9d528c81 100644
--- a/src/Symfony/Component/Yaml/Tests/ParserTest.php
+++ b/src/Symfony/Component/Yaml/Tests/ParserTest.php
@@ -1819,9 +1819,59 @@ public function testParserCleansUpReferencesBetweenRuns()
 YAML;
         $this->parser->parse($yaml);
     }
+
+    public function testPhpConstantTagMappingKey()
+    {
+        $yaml = <<<YAML
+transitions:
+    !php/const:Symfony\Component\Yaml\Tests\B::FOO:
+        from:
+            - !php/const:Symfony\Component\Yaml\Tests\B::BAR
+        to: !php/const:Symfony\Component\Yaml\Tests\B::BAZ
+YAML;
+        $expected = array(
+            'transitions' => array(
+                'foo' => array(
+                    'from' => array(
+                        'bar',
+                    ),
+                    'to' => 'baz',
+                ),
+            ),
+        );
+
+        $this->assertSame($expected, $this->parser->parse($yaml, Yaml::PARSE_CONSTANT));
+    }
+
+    public function testPhpConstantTagMappingKeyWithKeysCastToStrings()
+    {
+        $yaml = <<<YAML
+transitions:
+    !php/const:Symfony\Component\Yaml\Tests\B::FOO:
+        from:
+            - !php/const:Symfony\Component\Yaml\Tests\B::BAR
+        to: !php/const:Symfony\Component\Yaml\Tests\B::BAZ
+YAML;
+        $expected = array(
+            'transitions' => array(
+                'foo' => array(
+                    'from' => array(
+                        'bar',
+                    ),
+                    'to' => 'baz',
+                ),
+            ),
+        );
+
+        $this->assertSame($expected, $this->parser->parse($yaml, Yaml::PARSE_CONSTANT | Yaml::PARSE_KEYS_AS_STRINGS));
+    }
 }
 
 class B
 {
     public $b = 'foo';
+
+    const FOO = 'foo';
+    const BAR = 'bar';
+    const BAZ = 'baz';
 }