diff --git README.txt README.txt
index 2154181..30d0056 100644
--- README.txt
+++ README.txt
@@ -30,6 +30,7 @@ REQUIREMENTS
 ------------
 
 - Drupal 7.0 RC 2 or later
+- PHP 5.3.0 or later
 - The latest development copy of Date Popup, part of the Date module [1]
 
 [1] http://drupal.org/project/date