diff -r 3f4e5a50733e -r ef0f6eb5cd7c master/slave.c
--- a/master/slave.c	Thu Sep 20 10:05:37 2007 +0000
+++ b/master/slave.c	Thu Sep 20 10:15:21 2007 +0000
@@ -1432,7 +1432,11 @@
         return -1;
     }
 
-    return ec_sync_add_pdo(sync, pdo);
+    if (ec_sync_add_pdo(sync, pdo))
+        return -1;
+
+    sync->alt_mapping = 1;
+    return 0;
 }
 
 /*****************************************************************************/