diff --git a/src/wp-admin/setup-config.php b/src/wp-admin/setup-config.php
index 098e5d0524..7ea9d0be02 100644
--- a/src/wp-admin/setup-config.php
+++ b/src/wp-admin/setup-config.php
@@ -349,7 +349,7 @@ switch ( $step ) {
 
 		$key = 0;
 		foreach ( $config_file as $line_num => $line ) {
-			if ( '$table_prefix =' == substr( $line, 0, 16 ) ) {
+			if ( '$table_prefix =' == substr( $line, 0, 15 ) ) {
 				$config_file[ $line_num ] = '$table_prefix = \'' . addcslashes( $prefix, "\\'" ) . "';\r\n";
 				continue;
 			}