diff --git a/framework/CHANGELOG.md b/framework/CHANGELOG.md
index da3fa47624..0fdaaab9d4 100644
--- a/framework/CHANGELOG.md
+++ b/framework/CHANGELOG.md
@@ -20,6 +20,7 @@ Yii Framework 2 Change Log
 - Bug #3194: Date formatter works only for timestamps in the year range 1970 to 2038 (kartik-v)
 - Bug #3204: `yii\di\Container` did not handle the `$config` parameter well in case when it does not have a default value (qiangxue)
 - Bug #3216: Fixed the bug that `yii.activeForm.destroy()` did not remove `submit` event handlers (qiangxue)
+- Bug #3236: Return value for DateTime->format('U') casted to double to allow correct date formatting (pgaultier)
 - Enh #2264: `CookieCollection::has()` will return false for expired or removed cookies (qiangxue)
 - Enh #2837: Error page now shows arguments in stack trace method calls (samdark)
 - Enh #3008: Added `Html::errorSummary()` (qiangxue)
diff --git a/framework/base/Formatter.php b/framework/base/Formatter.php
index c958112892..b22ce4e3b2 100644
--- a/framework/base/Formatter.php
+++ b/framework/base/Formatter.php
@@ -357,11 +357,11 @@ class Formatter extends Component
                 } catch (\Exception $e) {
                     return false;
                 }
-                $value = $date->format('U');
+                $value = (double)$date->format('U');
             }
             return $value;
         } elseif ($value instanceof DateTime || $value instanceof \DateTimeInterface) {
-            return $value->format('U');
+            return (double)$value->format('U');
         } else {
             return (double)$value;
         }