--- a/master/domain.c	Thu Dec 23 09:48:56 2010 +0100
+++ b/master/domain.c	Wed Jan 05 08:36:53 2011 +0100
@@ -381,14 +381,14 @@
     EC_MASTER_DBG(domain->master, 1, "ecrt_domain_external_memory("
             "domain = 0x%p, mem = 0x%p)\n", domain, mem);
 
-    down(&domain->master->master_sem);
+    ec_mutex_lock(&domain->master->master_mutex);
 
     ec_domain_clear_data(domain);
 
     domain->data = mem;
     domain->data_origin = EC_ORIG_EXTERNAL;
 
-    up(&domain->master->master_sem);
+    ec_mutex_unlock(&domain->master->master_mutex);
 }
 
 /*****************************************************************************/