Index: typo3/install/index.php
===================================================================
--- typo3/install/index.php	(revision 5665)
+++ typo3/install/index.php	(working copy)
@@ -57,7 +57,13 @@
 }
 
 	// Change 1==2 to 1==1 if you want to lock the Install Tool regardless of the file ENABLE_INSTALL_TOOL
-if (1==2 || ($_SERVER['REMOTE_ADDR']!='127.0.0.1' && !is_file($enableInstallToolFile))) {
+if (1==2
+		|| (
+			($_SERVER['REMOTE_ADDR'] != '127.0.0.1')
+			&& ($_SERVER['REMOTE_ADDR'] != '::1')
+			&& (!is_file($enableInstallToolFile))
+		)
+) {
 	die(nl2br('<strong>The Install Tool is locked.</strong>
 
 		Fix: Create a file typo3conf/ENABLE_INSTALL_TOOL