diff --git a/src/view/form/control/AphrontFormDateControlValue.php b/src/view/form/control/AphrontFormDateControlValue.php
--- a/src/view/form/control/AphrontFormDateControlValue.php
+++ b/src/view/form/control/AphrontFormDateControlValue.php
@@ -182,7 +182,7 @@
       return null;
     }
 
-    return $datetime->format('U');
+    return (int)$datetime->format('U');
   }
 
   private function getTimeFormat() {