Index: wp-admin/includes/upgrade.php
===================================================================
--- wp-admin/includes/upgrade.php	(revision 15130)
+++ wp-admin/includes/upgrade.php	(working copy)
@@ -1402,7 +1402,7 @@
 			if ( array_key_exists(strtolower($table), $cqueries) ) {
 				// Clear the field and index arrays
 				unset($cfields);
-				unset($indices);
+				$indices = array();
 				// Get all of the field names in the query from between the parens
 				preg_match("|\((.*)\)|ms", $cqueries[strtolower($table)], $match2);
 				$qryline = trim($match2[1]);