diff --git a/Request.php b/Request.php
index f4ea78bbe..0e23d77f1 100644
--- a/Request.php
+++ b/Request.php
@@ -1290,19 +1290,37 @@ public function setMethod($method)
      */
     public function getMethod()
     {
-        if (null === $this->method) {
-            $this->method = strtoupper($this->server->get('REQUEST_METHOD', 'GET'));
-
-            if ('POST' === $this->method) {
-                if ($method = $this->headers->get('X-HTTP-METHOD-OVERRIDE')) {
-                    $this->method = strtoupper($method);
-                } elseif (self::$httpMethodParameterOverride) {
-                    $this->method = strtoupper($this->request->get('_method', $this->query->get('_method', 'POST')));
-                }
-            }
+        if (null !== $this->method) {
+            return $this->method;
+        }
+
+        $this->method = strtoupper($this->server->get('REQUEST_METHOD', 'GET'));
+
+        if ('POST' !== $this->method) {
+            return $this->method;
+        }
+
+        $method = $this->headers->get('X-HTTP-METHOD-OVERRIDE');
+
+        if (!$method && self::$httpMethodParameterOverride) {
+            $method = $this->request->get('_method', $this->query->get('_method', 'POST'));
+        }
+
+        if (!\is_string($method)) {
+            return $this->method;
+        }
+
+        $method = strtoupper($method);
+
+        if (\in_array($method, array('GET', 'HEAD', 'POST', 'PUT', 'DELETE', 'CONNECT', 'OPTIONS', 'PATCH', 'PURGE', 'TRACE'), true)) {
+            return $this->method = $method;
+        }
+
+        if (!preg_match('/^[A-Z]++$/D', $method)) {
+            throw new \UnexpectedValueException(sprintf('Invalid method override "%s".', $method));
         }
 
-        return $this->method;
+        return $this->method = $method;
     }
 
     /**