diff -ur Yap-5.1.2.orig/OPTYap/opt.structs.h Yap-5.1.2/OPTYap/opt.structs.h
--- Yap-5.1.2.orig/OPTYap/opt.structs.h	2007-05-02 07:33:53.000000000 +1200
+++ Yap-5.1.2/OPTYap/opt.structs.h	2007-08-21 19:44:56.000000000 +1200
@@ -41,7 +41,7 @@
 ** ---------------------- */
 
 struct pages {
-#ifdef YAPOR
+#if defined(YAPOR) || defined(THREADS)
   lockvar lock;
 #endif /* YAPOR */
   volatile long pages_allocated;
@@ -275,9 +275,11 @@
 ** --------------------------- */
 
 struct local_data{
+#if defined(YAPOR) || defined(THREADS)
+  lockvar lock;
+#endif
 #ifdef YAPOR
   /* local data related to or-parallelism */
-  lockvar lock;
   volatile int load;
   choiceptr top_choice_point;
   struct or_frame *top_or_frame;
diff -ur Yap-5.1.2.orig/OPTYap/tab.structs.h Yap-5.1.2/OPTYap/tab.structs.h
--- Yap-5.1.2.orig/OPTYap/tab.structs.h	2005-08-05 06:06:35.000000000 +1200
+++ Yap-5.1.2/OPTYap/tab.structs.h	2007-08-21 19:30:06.000000000 +1200
@@ -50,7 +50,7 @@
 ** ---------------------------- */
 
 typedef struct table_entry {
-#ifdef YAPOR
+#if defined(YAPOR) || defined(THREADS)
   lockvar lock;
 #endif /* YAPOR */
   struct pred_entry *pred_entry;
@@ -149,8 +149,10 @@
 ** ------------------------------ */
 
 typedef struct subgoal_frame {
-#ifdef YAPOR
+#if defined(YAPOR) || defined(THREADS)
   lockvar lock;
+#endif
+#ifdef YAPOR
   int generator_worker;
   struct or_frame *top_or_frame_on_generator_branch;
 #endif /* YAPOR */
@@ -225,8 +227,10 @@
 ** --------------------------------- */
 
 typedef struct dependency_frame {
-#ifdef YAPOR
+#if defined(YAPOR) || defined(THREADS)
   lockvar lock;
+#endif
+#ifdef YAPOR
   int leader_dependency_is_on_stack;
   struct or_frame *top_or_frame;
 #ifdef TIMESTAMP_CHECK