diff --git a/core/lib/Drupal/Core/Routing/ContentTypeHeaderMatcher.php b/core/lib/Drupal/Core/Routing/ContentTypeHeaderMatcher.php
index e7efcdd67b2edc098ca2511197be638ba4894502..13e18f35a9411b07eae2f792290d1d132cef9106 100644
--- a/core/lib/Drupal/Core/Routing/ContentTypeHeaderMatcher.php
+++ b/core/lib/Drupal/Core/Routing/ContentTypeHeaderMatcher.php
@@ -42,7 +42,12 @@ public function filter(RouteCollection $collection, Request $request) {
     // We do not throw a
     // \Symfony\Component\Routing\Exception\ResourceNotFoundException here
     // because we don't want to return a 404 status code, but rather a 415.
-    throw new UnsupportedMediaTypeHttpException('No route found that matches "Content-Type: ' . $request->headers->get('Content-Type') . '"');
+    if (!$request->headers->has('Content-Type')) {
+      throw new UnsupportedMediaTypeHttpException('No "Content-Type" request header specified');
+    }
+    else {
+      throw new UnsupportedMediaTypeHttpException('No route found that matches "Content-Type: ' . $request->headers->get('Content-Type') . '"');
+    }
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Core/Routing/ContentTypeHeaderMatcherTest.php b/core/tests/Drupal/Tests/Core/Routing/ContentTypeHeaderMatcherTest.php
index ec9783886989ebd348f5d5067be04d01c5750b30..13a9048f5001477935cccd80a873fddc32a1f508 100644
--- a/core/tests/Drupal/Tests/Core/Routing/ContentTypeHeaderMatcherTest.php
+++ b/core/tests/Drupal/Tests/Core/Routing/ContentTypeHeaderMatcherTest.php
@@ -4,12 +4,16 @@
 
 use Drupal\Core\Routing\ContentTypeHeaderMatcher;
 use Drupal\Tests\UnitTestCase;
+use Symfony\Component\HttpFoundation\ParameterBag;
 use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpKernel\Exception\UnsupportedMediaTypeHttpException;
 
 /**
  * Confirm that the content types partial matcher is functioning properly.
  *
  * @group Routing
+ *
+ * @coversDefaultClass \Drupal\Core\Routing\ContentTypeHeaderMatcher
  */
 class ContentTypeHeaderMatcherTest extends UnitTestCase {
 
@@ -88,8 +92,7 @@ public function testPostForm() {
   /**
    * Confirms that the matcher throws an exception for no-route.
    *
-   * @expectedException \Symfony\Component\HttpKernel\Exception\UnsupportedMediaTypeHttpException
-   * @expectedExceptionMessage No route found that matches "Content-Type: application/hal+json"
+   * @covers ::filter
    */
   public function testNoRouteFound() {
     $matcher = new ContentTypeHeaderMatcher();
@@ -97,8 +100,24 @@ public function testNoRouteFound() {
     $routes = $this->fixtures->contentRouteCollection();
     $request = Request::create('path/two', 'POST');
     $request->headers->set('Content-type', 'application/hal+json');
+    $this->setExpectedException(UnsupportedMediaTypeHttpException::class, 'No route found that matches "Content-Type: application/hal+json"');
+    $matcher->filter($routes, $request);
+  }
+
+  /**
+   * Confirms that the matcher throws an exception for missing request header.
+   *
+   * @covers ::filter
+   */
+  public function testContentTypeRequestHeaderMissing() {
+    $matcher = new ContentTypeHeaderMatcher();
+
+    $routes = $this->fixtures->contentRouteCollection();
+    $request = Request::create('path/two', 'POST');
+    // Delete all request headers that Request::create() sets by default.
+    $request->headers = new ParameterBag();
+    $this->setExpectedException(UnsupportedMediaTypeHttpException::class, 'No "Content-Type" request header specified.');
     $matcher->filter($routes, $request);
-    $this->fail('No exception was thrown.');
   }
 
 }