diff --git a/src/Symfony/Component/Yaml/Inline.php b/src/Symfony/Component/Yaml/Inline.php
index b0d6a031f8..2242d12c7b 100644
--- a/src/Symfony/Component/Yaml/Inline.php
+++ b/src/Symfony/Component/Yaml/Inline.php
@@ -350,19 +350,37 @@ class Inline
                 switch ($mapping[$i]) {
                     case '[':
                         // nested sequence
-                        $output[$key] = self::parseSequence($mapping, $i);
+                        $value = self::parseSequence($mapping, $i);
+                        // Spec: Keys MUST be unique; first one wins.
+                        // Parser cannot abort this mapping earlier, since lines
+                        // are processed sequentially.
+                        if (!isset($output[$key])) {
+                            $output[$key] = $value;
+                        }
                         $done = true;
                         break;
                     case '{':
                         // nested mapping
-                        $output[$key] = self::parseMapping($mapping, $i);
+                        $value = self::parseMapping($mapping, $i);
+                        // Spec: Keys MUST be unique; first one wins.
+                        // Parser cannot abort this mapping earlier, since lines
+                        // are processed sequentially.
+                        if (!isset($output[$key])) {
+                            $output[$key] = $value;
+                        }
                         $done = true;
                         break;
                     case ':':
                     case ' ':
                         break;
                     default:
-                        $output[$key] = self::parseScalar($mapping, array(',', '}'), array('"', "'"), $i);
+                        $value = self::parseScalar($mapping, array(',', '}'), array('"', "'"), $i);
+                        // Spec: Keys MUST be unique; first one wins.
+                        // Parser cannot abort this mapping earlier, since lines
+                        // are processed sequentially.
+                        if (!isset($output[$key])) {
+                            $output[$key] = $value;
+                        }
                         $done = true;
                         --$i;
                 }
diff --git a/src/Symfony/Component/Yaml/Parser.php b/src/Symfony/Component/Yaml/Parser.php
index 9bde67b57b..9539e36aa3 100644
--- a/src/Symfony/Component/Yaml/Parser.php
+++ b/src/Symfony/Component/Yaml/Parser.php
@@ -178,18 +178,35 @@ class Parser
                 } elseif (!isset($values['value']) || '' == trim($values['value'], ' ') || 0 === strpos(ltrim($values['value'], ' '), '#')) {
                     // if next line is less indented or equal, then it means that the current value is null
                     if (!$this->isNextLineIndented() && !$this->isNextLineUnIndentedCollection()) {
-                        $data[$key] = null;
+                        // Spec: Keys MUST be unique; first one wins.
+                        // Parser cannot abort this mapping earlier, since lines
+                        // are processed sequentially.
+                        if (!isset($data[$key])) {
+                            $data[$key] = null;
+                        }
                     } else {
                         $c = $this->getRealCurrentLineNb() + 1;
                         $parser = new Parser($c);
                         $parser->refs =& $this->refs;
-                        $data[$key] = $parser->parse($this->getNextEmbedBlock(), $exceptionOnInvalidType, $objectSupport);
+                        $value = $parser->parse($this->getNextEmbedBlock(), $exceptionOnInvalidType, $objectSupport);
+                        // Spec: Keys MUST be unique; first one wins.
+                        // Parser cannot abort this mapping earlier, since lines
+                        // are processed sequentially.
+                        if (!isset($data[$key])) {
+                            $data[$key] = $value;
+                        }
                     }
                 } else {
                     if ($isInPlace) {
                         $data = $this->refs[$isInPlace];
                     } else {
-                        $data[$key] = $this->parseValue($values['value'], $exceptionOnInvalidType, $objectSupport);
+                        $value = $this->parseValue($values['value'], $exceptionOnInvalidType, $objectSupport);;
+                        // Spec: Keys MUST be unique; first one wins.
+                        // Parser cannot abort this mapping earlier, since lines
+                        // are processed sequentially.
+                        if (!isset($data[$key])) {
+                            $data[$key] = $value;
+                        }
                     }
                 }
             } else {
diff --git a/src/Symfony/Component/Yaml/Tests/ParserTest.php b/src/Symfony/Component/Yaml/Tests/ParserTest.php
index 2335efc559..a4db960729 100644
--- a/src/Symfony/Component/Yaml/Tests/ParserTest.php
+++ b/src/Symfony/Component/Yaml/Tests/ParserTest.php
@@ -508,6 +508,53 @@ EOF
         );
     }
 
+    /**
+     * > It is an error for two equal keys to appear in the same mapping node.
+     * > In such a case the YAML processor may continue, ignoring the second
+     * > `key: value` pair and issuing an appropriate warning. This strategy
+     * > preserves a consistent information model for one-pass and random access
+     * > applications.
+     *
+     * @see http://yaml.org/spec/1.2/spec.html#id2759572
+     * @see http://yaml.org/spec/1.1/#id932806
+     *
+     * @covers \Symfony\Component\Yaml\Parser::parse
+     */
+    public function testMappingDuplicateKeyBlock()
+    {
+        $input = <<<EOD
+parent:
+    child: first
+    child: duplicate
+parent:
+    child: duplicate
+    child: duplicate
+EOD;
+        $expected = array(
+            'parent' => array(
+                'child' => 'first',
+            ),
+        );
+        $this->assertSame($expected, Yaml::parse($input));
+    }
+
+    /**
+     * @covers \Symfony\Component\Yaml\Inline::parseMapping
+     */
+    public function testMappingDuplicateKeyFlow()
+    {
+        $input = <<<EOD
+parent: { child: first, child: duplicate }
+parent: { child: duplicate, child: duplicate }
+EOD;
+        $expected = array(
+            'parent' => array(
+                'child' => 'first',
+            ),
+        );
+        $this->assertSame($expected, Yaml::parse($input));
+    }
+
     public function testEmptyValue()
     {
         $input = <<<EOF