diff --git a/src/MessageTrait.php b/src/MessageTrait.php
index 17bc2d29..7647c29a 100644
--- a/src/MessageTrait.php
+++ b/src/MessageTrait.php
@@ -70,6 +70,7 @@ public function getProtocolVersion()
      */
     public function withProtocolVersion($version)
     {
+        $this->validateProtocolVersion($version);
         $new = clone $this;
         $new->protocol = $version;
         return $new;
@@ -400,4 +401,32 @@ private static function assertValidHeaderValue(array $values)
     {
         array_walk($values, __NAMESPACE__ . '\HeaderSecurity::assertValid');
     }
+
+    /**
+     * Validate the HTTP protocol version
+     *
+     * @param string $version
+     * @throws InvalidArgumentException on invalid HTTP protocol version
+     */
+    private function validateProtocolVersion($version)
+    {
+        if (empty($version)) {
+            throw new InvalidArgumentException(sprintf(
+                'HTTP protocol version can not be empty'
+            ));
+        }
+        if (! is_string($version)) {
+            throw new InvalidArgumentException(sprintf(
+                'Unsupported HTTP protocol version; must be a string, received %s',
+                (is_object($version) ? get_class($version) : gettype($version))
+            ));
+        }
+        //HTTP uses a "<major>.<minor>" numbering scheme to indicate versions of the protocol
+        if (! preg_match('~^\d+\.\d+$~', $version)) {
+            throw new InvalidArgumentException(sprintf(
+                'Unsupported HTTP protocol version "%s" provided',
+                $version
+            ));
+        }
+    }
 }
diff --git a/src/Request/Serializer.php b/src/Request/Serializer.php
index d7c8d131..b7ef5350 100644
--- a/src/Request/Serializer.php
+++ b/src/Request/Serializer.php
@@ -76,6 +76,10 @@ public static function fromStream(StreamInterface $stream)
      */
     public static function toString(RequestInterface $request)
     {
+        $httpMethod = $request->getMethod();
+        if (empty($httpMethod)) {
+            throw new UnexpectedValueException('Object can not be serialized because HTTP method is empty');
+        }
         $headers = self::serializeHeaders($request->getHeaders());
         $body    = (string) $request->getBody();
         $format  = '%s %s HTTP/%s%s%s';
@@ -89,7 +93,7 @@ public static function toString(RequestInterface $request)
 
         return sprintf(
             $format,
-            $request->getMethod(),
+            $httpMethod,
             $request->getRequestTarget(),
             $request->getProtocolVersion(),
             $headers,
diff --git a/test/MessageTraitTest.php b/test/MessageTraitTest.php
index 500eb1c4..26b8ebc4 100644
--- a/test/MessageTraitTest.php
+++ b/test/MessageTraitTest.php
@@ -39,6 +39,30 @@ public function testProtocolMutatorReturnsCloneWithChanges()
         $this->assertEquals('1.0', $message->getProtocolVersion());
     }
 
+
+    public function invalidProtocolVersionProvider()
+    {
+        return [
+            'true'     => [ true ],
+            'false'    => [ false ],
+            'int'      => [ 1 ],
+            'float'    => [ 1.1 ],
+            'array'    => [ ['1.1'] ],
+            'stdClass' => [ (object) [ 'version' => '1.0'] ],
+            'wrong-format' => [ '1'],
+            'wrong-format2' => [ '1.2.3'],
+        ];
+    }
+    /**
+     * @dataProvider invalidProtocolVersionProvider
+     */
+    public function testWithProtocolVersionRaisesExceptionForInvalidVersion($version)
+    {
+        $this->setExpectedException('InvalidArgumentException');
+        $request = new Request();
+        $request->withProtocolVersion($version);
+    }
+
     public function testUsesStreamProvidedInConstructorAsBody()
     {
         $stream  = $this->getMock('Psr\Http\Message\StreamInterface');
diff --git a/test/Request/SerializerTest.php b/test/Request/SerializerTest.php
index 462433c6..ba1ed2a9 100644
--- a/test/Request/SerializerTest.php
+++ b/test/Request/SerializerTest.php
@@ -15,6 +15,7 @@
 use Zend\Diactoros\Request\Serializer;
 use Zend\Diactoros\Stream;
 use Zend\Diactoros\Uri;
+use UnexpectedValueException;
 
 class SerializerTest extends TestCase
 {
@@ -326,4 +327,14 @@ public function testFromStreamStopsReadingAfterScanningHeader()
         $stream = Serializer::fromStream($stream);
         $this->assertInstanceOf('Zend\Diactoros\RelativeStream', $stream->getBody());
     }
+
+    /**
+     * @expectedException UnexpectedValueException
+     */
+    public function testToStringRaisesExceptionOnEmptyMethod()
+    {
+        $request = (new Request())
+            ->withUri(new Uri('http://example.com/foo/bar?baz=bat'));
+        $message = Serializer::toString($request);
+    }
 }