diff --git a/src/Symfony/Component/Yaml/Inline.php b/src/Symfony/Component/Yaml/Inline.php
index b4a7072228e9b..ec3392161447c 100644
--- a/src/Symfony/Component/Yaml/Inline.php
+++ b/src/Symfony/Component/Yaml/Inline.php
@@ -458,7 +458,10 @@ private static function parseMapping($mapping, $flags, &$i = 0, $references = ar
 
             // key
             $key = self::parseScalar($mapping, $flags, array(':', ' '), array('"', "'"), $i, false);
-            $i = strpos($mapping, ':', $i);
+
+            if (false === $i = strpos($mapping, ':', $i)) {
+                break;
+            }
 
             if (!isset($mapping[$i + 1]) || ' ' !== $mapping[$i + 1]) {
                 @trigger_error('Omitting the space after the colon that follows a mapping key definition is deprecated since version 3.2 and will throw a ParseException in 4.0.', E_USER_DEPRECATED);
diff --git a/src/Symfony/Component/Yaml/Tests/InlineTest.php b/src/Symfony/Component/Yaml/Tests/InlineTest.php
index 35cd6b73aad20..22a3964809144 100644
--- a/src/Symfony/Component/Yaml/Tests/InlineTest.php
+++ b/src/Symfony/Component/Yaml/Tests/InlineTest.php
@@ -654,4 +654,13 @@ public function getInvalidBinaryData()
             'misplaced equals character' => array('!!binary "SGVsbG8gd29ybG=Q"', '/The base64 encoded data \(.*\) contains invalid characters/'),
         );
     }
+
+    /**
+     * @expectedException \Symfony\Component\Yaml\Exception\ParseException
+     * @expectedExceptionMessage Malformed inline YAML string {this, is not, yaml}
+     */
+    public function testStringOffsetCastError()
+    {
+        Inline::parse('{this, is not, yaml}');
+    }
 }