diff --git a/core/modules/rest/src/Plugin/views/display/RestExport.php b/core/modules/rest/src/Plugin/views/display/RestExport.php
index 582a9c4719..d2f66fff95 100644
--- a/core/modules/rest/src/Plugin/views/display/RestExport.php
+++ b/core/modules/rest/src/Plugin/views/display/RestExport.php
@@ -139,14 +139,22 @@ public static function create(ContainerInterface $container, array $configuratio
   public function initDisplay(ViewExecutable $view, array &$display, array &$options = NULL) {
     parent::initDisplay($view, $display, $options);
 
+    // If the default 'json' format is not selected as a format option in the
+    // view display, fallback to the first format available for the default.
+    if (!empty($options['style']['options']['formats']) && !isset($options['style']['options']['formats'][$this->getContentType()])) {
+      $default_format = reset($options['style']['options']['formats']);
+      $this->setContentType($default_format);
+    }
+
+    // Only use the requested content type if it's not 'html'. This allows
+    // still falling back to the default for things like views preview.
     $request_content_type = $this->view->getRequest()->getRequestFormat();
 
-    // This allows still falling back to the default for things like views
-    // preview.
     if ($request_content_type !== 'html') {
       $this->setContentType($request_content_type);
-      $this->setMimeType($this->view->getRequest()->getMimeType($request_content_type));
     }
+
+    $this->setMimeType($this->view->getRequest()->getMimeType($this->getContentType()));
   }
 
   /**
diff --git a/core/modules/rest/src/Tests/Views/StyleSerializerTest.php b/core/modules/rest/src/Tests/Views/StyleSerializerTest.php
index 6e04d6b96e..5711b7b865 100644
--- a/core/modules/rest/src/Tests/Views/StyleSerializerTest.php
+++ b/core/modules/rest/src/Tests/Views/StyleSerializerTest.php
@@ -176,6 +176,11 @@ public function testSerializerResponses() {
     $this->assertCacheTags($expected_cache_tags);
     $this->assertCacheContexts(['languages:language_interface', 'theme', 'entity_test_view_grants', 'request_format']);
 
+    // This should fall back to JSON.
+    $actual_json = $this->drupalGet('test/serialize/entity');
+    $this->assertResponse(200);
+    $this->assertIdentical($actual_json, $expected, 'The expected JSON output was found.');
+
     $expected = $serializer->serialize($entities, 'hal_json');
     $actual_json = $this->drupalGetWithFormat('test/serialize/entity', 'hal_json');
     $this->assertIdentical($actual_json, $expected, 'The expected HAL output was found.');
@@ -195,9 +200,15 @@ public function testSerializerResponses() {
     $view->save();
     $expected = $serializer->serialize($entities, 'xml');
     $actual_xml = $this->drupalGetWithFormat('test/serialize/entity', 'xml');
+    $this->assertResponse(200);
     $this->assertIdentical($actual_xml, $expected, 'The expected XML output was found.');
     $this->assertCacheContexts(['languages:language_interface', 'theme', 'entity_test_view_grants', 'request_format']);
 
+    // This should fall back to XML.
+    $actual_xml = $this->drupalGetWithFormat('test/serialize/entity');
+    $this->assertResponse(200);
+    $this->assertIdentical($actual_xml, $expected, 'The expected XML output was found.');
+
     // Allow multiple formats.
     $view->setDisplay('rest_export_1');
     $view->getDisplay()->setOption('style', [
@@ -348,6 +359,11 @@ public function testResponseFormatConfiguration() {
 
     $style_options = 'admin/structure/views/nojs/display/test_serializer_display_field/rest_export_1/style_options';
 
+    // Test with no format.
+    $this->drupalGet('test/serialize/field');
+    $this->assertHeader('content-type', 'application/json');
+    $this->assertResponse(406, 'A 406 response was returned when no format was requested.');
+
     // Select only 'xml' as an accepted format.
     $this->drupalPostForm($style_options, ['style_options[formats][xml]' => 'xml'], t('Apply'));
     $this->drupalPostForm(NULL, [], t('Save'));
@@ -365,12 +381,6 @@ public function testResponseFormatConfiguration() {
     $this->drupalPostForm($style_options, ['style_options[formats][json]' => 'json'], t('Apply'));
     $this->drupalPostForm(NULL, [], t('Save'));
 
-    // Should return a 200.
-    // @todo This should be fixed when we have better content negotiation.
-    $this->drupalGetWithFormat('test/serialize/field', 'json');
-    $this->assertHeader('content-type', 'application/json');
-    $this->assertResponse(200, 'A 200 response was returned when any format was requested.');
-
     // Should return a 406. Emulates a sample Firefox header.
     $this->drupalGet('test/serialize/field', [], ['Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8']);
     $this->assertHeader('content-type', 'text/html; charset=UTF-8');