diff --git a/framework/CHANGELOG.md b/framework/CHANGELOG.md
index 8a0ce3e16e..48f5334bcb 100644
--- a/framework/CHANGELOG.md
+++ b/framework/CHANGELOG.md
@@ -26,6 +26,7 @@ Yii Framework 2 Change Log
 - Enh #11979: Added `yii\mutex\OracleMutex` which implements mutex "lock" mechanism via Oracle locks (zlakomanoff)
 - Enh #12082: Used `jQuery.on(` instead of event method to ensure forwards compatibility (newerton)
 - Enh #12028: Add -h|--help option to console command to display help information (pana1990)
+- Enh #12099: HttpCache no longer returns 304 HTTP code when callbacks return null (sergeymakinen)
 - Bug #12053: `./yii migrate/create` was generating wrong code when using `bigPrimaryKey` (VojtechH, samdark)
 - Bug #11907: Fixed `yii\helpers\Console::getScreenSize()` on Windows was giving out width and height swapped (Spell6inder, samdark, cebe)
 - Bug #11973: Fixed `yii\helpers\BaseHtml::getAttributeValue()` to work with `items[]` notation correctly (silverfire)
diff --git a/framework/filters/HttpCache.php b/framework/filters/HttpCache.php
index 8df842f78b..072df0d941 100644
--- a/framework/filters/HttpCache.php
+++ b/framework/filters/HttpCache.php
@@ -130,7 +130,9 @@ class HttpCache extends ActionFilter
         }
         if ($this->etagSeed !== null) {
             $seed = call_user_func($this->etagSeed, $action, $this->params);
-            $etag = $this->generateEtag($seed);
+            if ($seed !== null) {
+                $etag = $this->generateEtag($seed);
+            }
         }
 
         $this->sendCacheControlHeader();
@@ -140,20 +142,22 @@ class HttpCache extends ActionFilter
             $response->getHeaders()->set('Etag', $etag);
         }
 
-        if ($this->validateCache($lastModified, $etag)) {
+        $cacheValid = $this->validateCache($lastModified, $etag);
+        // https://tools.ietf.org/html/rfc7232#section-4.1
+        if ($lastModified !== null && (!$cacheValid || ($cacheValid && $etag === null))) {
+            $response->getHeaders()->set('Last-Modified', gmdate('D, d M Y H:i:s', $lastModified) . ' GMT');
+        }
+        if ($cacheValid) {
             $response->setStatusCode(304);
             return false;
         }
 
-        if ($lastModified !== null) {
-            $response->getHeaders()->set('Last-Modified', gmdate('D, d M Y H:i:s', $lastModified) . ' GMT');
-        }
-
         return true;
     }
 
     /**
      * Validates if the HTTP cache contains valid content.
+     * If both Last-Modified and ETag are null, returns false.
      * @param integer $lastModified the calculated Last-Modified value in terms of a UNIX timestamp.
      * If null, the Last-Modified header will not be validated.
      * @param string $etag the calculated ETag value. If null, the ETag header will not be validated.
@@ -168,7 +172,7 @@ class HttpCache extends ActionFilter
         } elseif (isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
             return $lastModified !== null && @strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) >= $lastModified;
         } else {
-            return $etag === null && $lastModified === null;
+            return false;
         }
     }
 
diff --git a/tests/framework/filters/HttpCacheTest.php b/tests/framework/filters/HttpCacheTest.php
index ecd354d5a2..c2234d7ca6 100644
--- a/tests/framework/filters/HttpCacheTest.php
+++ b/tests/framework/filters/HttpCacheTest.php
@@ -38,7 +38,7 @@ class HttpCacheTest extends \yiiunit\TestCase
         $method->setAccessible(true);
 
         unset($_SERVER['HTTP_IF_MODIFIED_SINCE'], $_SERVER['HTTP_IF_NONE_MATCH']);
-        $this->assertTrue($method->invoke($httpCache, null, null));
+        $this->assertFalse($method->invoke($httpCache, null, null));
         $this->assertFalse($method->invoke($httpCache, 0, null));
         $this->assertFalse($method->invoke($httpCache, 0, '"foo"'));
 
@@ -65,6 +65,14 @@ class HttpCacheTest extends \yiiunit\TestCase
     {
         $httpCache = new HttpCache;
         $httpCache->weakEtag = false;
+
+        $httpCache->etagSeed = function($action, $params) {
+            return null;
+        };
+        $httpCache->beforeAction(null);
+        $response = Yii::$app->getResponse();
+        $this->assertFalse($response->getHeaders()->offsetExists('ETag'));
+
         $httpCache->etagSeed = function($action, $params) {
             return '';
         };