diff --git a/contrib/10.callcc/callcc.c b/contrib/10.callcc/callcc.c
index 6c62741e..ce9db7c7 100644
--- a/contrib/10.callcc/callcc.c
+++ b/contrib/10.callcc/callcc.c
@@ -20,7 +20,7 @@ struct fullcont {
   size_t ci_offset;
   ptrdiff_t ci_len;
 
-  struct code *ip;
+  const struct code *ip;
 
   struct object **arena;
   size_t arena_size, arena_idx;
diff --git a/extlib/benz/cont.c b/extlib/benz/cont.c
index 02fd42e6..6eff9709 100644
--- a/extlib/benz/cont.c
+++ b/extlib/benz/cont.c
@@ -13,7 +13,7 @@ struct cont {
   ptrdiff_t sp_offset;
   ptrdiff_t ci_offset;
   size_t arena_idx;
-  struct code *ip;
+  const struct code *ip;
 
   int retc;
   pic_value *retv;
diff --git a/extlib/benz/include/picrin/private/state.h b/extlib/benz/include/picrin/private/state.h
index a779f43e..06b63118 100644
--- a/extlib/benz/include/picrin/private/state.h
+++ b/extlib/benz/include/picrin/private/state.h
@@ -23,7 +23,7 @@ struct lib {
 
 struct callinfo {
   int argc, retc;
-  struct code *ip;
+  const struct code *ip;
   pic_value *fp;
   struct irep *irep;
   struct context *cxt;
@@ -48,7 +48,7 @@ struct pic_state {
   struct callinfo *ci;
   struct callinfo *cibase, *ciend;
 
-  struct code *ip;
+  const struct code *ip;
 
   const char *lib;
 
@@ -62,7 +62,6 @@ struct pic_state {
   struct list_head ireps;
 
   xFILE files[XOPEN_MAX];
-  struct code iseq[2];          /* for pic_apply_trampoline */
 
   bool gc_enable;
   struct heap *heap;
diff --git a/extlib/benz/proc.c b/extlib/benz/proc.c
index a097d3b7..a77814e0 100644
--- a/extlib/benz/proc.c
+++ b/extlib/benz/proc.c
@@ -783,15 +783,11 @@ pic_apply(pic_state *pic, pic_value proc, int argc, pic_value *argv)
 pic_value
 pic_applyk(pic_state *pic, pic_value proc, int argc, pic_value *args)
 {
+  static const struct code iseq[2] = { { OP_NOP, 0, 0 }, { OP_TAILCALL, -1, 0 } };
   pic_value *sp;
   struct callinfo *ci;
   int i;
 
-  pic->iseq[0].insn = OP_NOP;
-  pic->iseq[0].a = 0;
-  pic->iseq[1].insn = OP_TAILCALL;
-  pic->iseq[1].a = -1;
-
   *pic->sp++ = proc;
 
   sp = pic->sp;
@@ -800,7 +796,7 @@ pic_applyk(pic_state *pic, pic_value proc, int argc, pic_value *args)
   }
 
   ci = PUSHCI();
-  ci->ip = pic->iseq;
+  ci->ip = iseq;
   ci->fp = pic->sp;
   ci->retc = (int)argc;