diff --git a/system/core/CodeIgniter.php b/system/core/CodeIgniter.php
index 2d3f249..0d0fffb 100644
--- a/system/core/CodeIgniter.php
+++ b/system/core/CodeIgniter.php
@@ -36,6 +36,13 @@
 
 /*
  * ------------------------------------------------------
+ *  Define the CodeIgniter Branch (Core = TRUE, Reactor = FALSE)
+ * ------------------------------------------------------
+ */
+	define('CI_CORE', TRUE);
+
+/*
+ * ------------------------------------------------------
  *  Load the global functions
  * ------------------------------------------------------
  */
diff --git a/user_guide/changelog.html b/user_guide/changelog.html
index 9f0e226..b113b0c 100644
--- a/user_guide/changelog.html
+++ b/user_guide/changelog.html
@@ -65,6 +65,7 @@
 	<li>General changes
 		<ul>
 			<li>Added <kbd>$config['cookie_secure']</kbd> to the config file to allow requiring a secure (HTTPS) in order to set cookies.</li>
+			<li class="reactor">Added the constant <kbd>CI_CORE</kbd> to help differentiate between Core: TRUE and Reactor: FALSE.</li>
 		</ul>
 	</li>
 	<li>Libraries