--- erl_bif_guard-orig.c	2010-02-19 18:04:28.000000000 +0000
+++ erl_bif_guard.c	2010-02-28 13:04:48.000000000 +0000
@@ -25,6 +25,8 @@
 #  include "config.h"
 #endif
 
+#define PREFETCH_LENGTH
+
 #include "sys.h"
 #include "erl_vm.h"
 #include "global.h"
@@ -161,7 +163,7 @@ BIF_RETTYPE round_1(BIF_ALIST_1)
 
 BIF_RETTYPE length_1(BIF_ALIST_1)
 {
-    Eterm list;
+    Eterm list, list2;
     Uint i;
      
     if (is_nil(BIF_ARG_1)) 
@@ -173,7 +175,11 @@ BIF_RETTYPE length_1(BIF_ALIST_1)
     i = 0;
     while (is_list(list)) {
 	i++;
-	list = CDR(list_val(list));
+	list2 = CDR(list_val(list));
+	#ifdef PREFETCH_LENGTH
+	__builtin_prefetch((char*)list2 + 128*((long)list2-(long)list));
+	#endif
+	list = list2;
     }
     if (is_not_nil(list))  {
 	BIF_ERROR(BIF_P, BADARG);
@@ -329,6 +335,7 @@ double_to_integer(Process* p, double x)
 Eterm erts_gc_length_1(Process* p, Eterm* reg, Uint live)
 {
     Eterm list = reg[live];
+    Eterm list2;
     int i;
 
     if (is_nil(list)) 
@@ -336,7 +343,11 @@ Eterm erts_gc_length_1(Process* p, Eterm
     i = 0;
     while (is_list(list)) {
 	i++;
-	list = CDR(list_val(list));
+	list2 = CDR(list_val(list));
+	#ifdef PREFETCH_LENGTH
+	__builtin_prefetch((char*)list2 + 128*((long)list2-(long)list));
+	#endif
+	list = list2;
     }
     if (is_not_nil(list))  {
 	BIF_ERROR(p, BADARG);