diff --git a/src/gdd/gddAppTable.cc b/src/gdd/gddAppTable.cc
index 92b0cacec..7a3890559 100644
--- a/src/gdd/gddAppTable.cc
+++ b/src/gdd/gddAppTable.cc
@@ -433,8 +433,10 @@ gddStatus gddApplicationTypeTable::freeDD(gdd* dd)
 		}
 
 		// fprintf(stderr,"Adding DD to free_list %d\n",app);
+		attr_table[group][app].sem.lock ();
 		dd->setNext(attr_table[group][app].free_list);
 		attr_table[group][app].free_list=dd;
+		attr_table[group][app].sem.unlock ();
 	}
 	else if (attr_table[group][app].type==gddApplicationTypeNormal)
 	{