diff --git a/bin/ikarus b/bin/ikarus
index dc749c7..dad761e 100755
Binary files a/bin/ikarus and b/bin/ikarus differ
diff --git a/bin/ikarus.h b/bin/ikarus.h
index 7e0bb55..ff84bbc 100644
--- a/bin/ikarus.h
+++ b/bin/ikarus.h
@@ -110,6 +110,7 @@ typedef struct ikpcb{
   void* system_stack;                 /* offset = 24 */
   unsigned int* dirty_vector;         /* offset = 28 */
   ikp   arg_list;                     /* offset = 32 */
+  ikp   engine_counter;               /* offset = 36 */
   /* the rest are not used by any scheme code        */
   /* they only support the runtime system (gc, etc.) */
   unsigned int* segment_vector; 
diff --git a/src/geninstr/gen.pl b/src/geninstr/gen.pl
index 13b6515..1543036 100755
--- a/src/geninstr/gen.pl
+++ b/src/geninstr/gen.pl
@@ -48,8 +48,7 @@ sub gen3{
   }
 }
 
-gen1 "movl \$27, 4(r1)\n";
-gen1 "movl \$27, 4000(r1)\n";
+gen1 "addl \$27, 12(r1)\n";
 
 #gen1 "movb \$0, 4(r1)\n";
 #gen1 "movb -2(r1), %ah\n";
diff --git a/src/geninstr/tmp.dump b/src/geninstr/tmp.dump
index 821d007..e69de29 100644
--- a/src/geninstr/tmp.dump
+++ b/src/geninstr/tmp.dump
@@ -1,31 +0,0 @@
-
-tmp.o:     file format elf32-i386
-
-Disassembly of section .text:
-
-00000000 <.text>:
-   0:	c7 40 04 1b 00 00 00 	movl   $0x1b,0x4(%eax)
-   7:	c7 41 04 1b 00 00 00 	movl   $0x1b,0x4(%ecx)
-   e:	c7 42 04 1b 00 00 00 	movl   $0x1b,0x4(%edx)
-  15:	c7 43 04 1b 00 00 00 	movl   $0x1b,0x4(%ebx)
-  1c:	c7 44 24 04 1b 00 00 	movl   $0x1b,0x4(%esp)
-  23:	00 
-  24:	c7 45 04 1b 00 00 00 	movl   $0x1b,0x4(%ebp)
-  2b:	c7 46 04 1b 00 00 00 	movl   $0x1b,0x4(%esi)
-  32:	c7 47 04 1b 00 00 00 	movl   $0x1b,0x4(%edi)
-  39:	c7 80 a0 0f 00 00 1b 	movl   $0x1b,0xfa0(%eax)
-  40:	00 00 00 
-  43:	c7 81 a0 0f 00 00 1b 	movl   $0x1b,0xfa0(%ecx)
-  4a:	00 00 00 
-  4d:	c7 82 a0 0f 00 00 1b 	movl   $0x1b,0xfa0(%edx)
-  54:	00 00 00 
-  57:	c7 83 a0 0f 00 00 1b 	movl   $0x1b,0xfa0(%ebx)
-  5e:	00 00 00 
-  61:	c7 84 24 a0 0f 00 00 	movl   $0x1b,0xfa0(%esp)
-  68:	1b 00 00 00 
-  6c:	c7 85 a0 0f 00 00 1b 	movl   $0x1b,0xfa0(%ebp)
-  73:	00 00 00 
-  76:	c7 86 a0 0f 00 00 1b 	movl   $0x1b,0xfa0(%esi)
-  7d:	00 00 00 
-  80:	c7 87 a0 0f 00 00 1b 	movl   $0x1b,0xfa0(%edi)
-  87:	00 00 00 
diff --git a/src/geninstr/tmp.s b/src/geninstr/tmp.s
index ea423d1..d828601 100644
--- a/src/geninstr/tmp.s
+++ b/src/geninstr/tmp.s
@@ -1,17 +1,9 @@
 .text
-movl $27, 4(%eax)
-movl $27, 4(%ecx)
-movl $27, 4(%edx)
-movl $27, 4(%ebx)
-movl $27, 4(%esp)
-movl $27, 4(%ebp)
-movl $27, 4(%esi)
-movl $27, 4(%edi)
-movl $27, 4000(%eax)
-movl $27, 4000(%ecx)
-movl $27, 4000(%edx)
-movl $27, 4000(%ebx)
-movl $27, 4000(%esp)
-movl $27, 4000(%ebp)
-movl $27, 4000(%esi)
-movl $27, 4000(%edi)
+addl $27, 12(%eax)
+addl $27, 12(%ecx)
+addl $27, 12(%edx)
+addl $27, 12(%ebx)
+addl $27, 12(%esp)
+addl $27, 12(%ebp)
+addl $27, 12(%esi)
+addl $27, 12(%edi)
diff --git a/src/ikarus.boot b/src/ikarus.boot
index 3239021..4032a70 100644
Binary files a/src/ikarus.boot and b/src/ikarus.boot differ
diff --git a/src/libcompile.ss b/src/libcompile.ss
index 5e28349..41d0d3a 100644
--- a/src/libcompile.ss
+++ b/src/libcompile.ss
@@ -2931,6 +2931,7 @@
       [(system-stack)       (mem 24 pcr)]
       [(dirty-vector)       (mem 28 pcr)]
       [(arg-list)           (mem 32 pcr)]
+      [(engine-counter)     (mem 36 pcr)]
       [else (error 'pcb-ref "invalid arg ~s" x)])))
 
 (define (primref-loc op)
diff --git a/src/libintelasm.ss b/src/libintelasm.ss
index 7168d32..89b2349 100644
--- a/src/libintelasm.ss
+++ b/src/libintelasm.ss
@@ -478,6 +478,8 @@
        (CODE #x01 (ModRM 3 src dst ac))]
       [(and (mem? src) (reg? dst))
        (CODErd #x03 dst src ac)]
+      [(and (imm? src) (mem? dst)) 
+       (CODEdi #x81 dst src ac)]
       [else (error who "invalid ~s" instr)])]
    [(subl src dst)
     (cond