diff --git a/contrib/10.callcc/callcc.c b/contrib/10.callcc/callcc.c
index 280b8331..cf1c310b 100644
--- a/contrib/10.callcc/callcc.c
+++ b/contrib/10.callcc/callcc.c
@@ -1,5 +1,6 @@
 #include "picrin.h"
 #include "picrin/object.h"
+#include "picrin/state.h"
 
 struct pic_fullcont {
   jmp_buf jmp;
diff --git a/etc/mkloader.pl b/etc/mkloader.pl
index 527efd7a..088bd962 100755
--- a/etc/mkloader.pl
+++ b/etc/mkloader.pl
@@ -53,7 +53,7 @@ EOL
   pic_catch {
     /* error! */
     xfputs(pic, "fatal error: failure in loading $dirname/$basename\\n", xstderr);
-    pic_raise(pic, pic->err);
+    pic_raise(pic, pic_err(pic));
   }
 EOL
 }
diff --git a/extlib/benz/cont.c b/extlib/benz/cont.c
index 0df3d685..21ffde89 100644
--- a/extlib/benz/cont.c
+++ b/extlib/benz/cont.c
@@ -4,6 +4,7 @@
 
 #include "picrin.h"
 #include "picrin/object.h"
+#include "picrin/state.h"
 
 struct pic_cont {
   PIC_JMPBUF *jmp;
diff --git a/extlib/benz/debug.c b/extlib/benz/debug.c
index 21a5211d..bc96a209 100644
--- a/extlib/benz/debug.c
+++ b/extlib/benz/debug.c
@@ -4,6 +4,7 @@
 
 #include "picrin.h"
 #include "picrin/object.h"
+#include "picrin/state.h"
 
 pic_value
 pic_get_backtrace(pic_state *pic)
@@ -36,16 +37,18 @@ pic_get_backtrace(pic_state *pic)
 void
 pic_print_backtrace(pic_state *pic, xFILE *file)
 {
-  assert(! pic_invalid_p(pic, pic->err));
+  pic_value err = pic_err(pic);
 
-  if (! pic_error_p(pic, pic->err)) {
+  assert(! pic_invalid_p(pic, err));
+
+  if (! pic_error_p(pic, err)) {
     xfprintf(pic, file, "raise: ");
-    pic_fwrite(pic, pic->err, file);
+    pic_fwrite(pic, err, file);
   } else {
     struct pic_error *e;
     pic_value elem, it;
 
-    e = pic_error_ptr(pic, pic->err);
+    e = pic_error_ptr(pic, err);
     if (! pic_eq_p(pic, pic_obj_value(e->type), pic_intern_lit(pic, ""))) {
       pic_fwrite(pic, pic_obj_value(e->type), file);
       xfprintf(pic, file, " ");
diff --git a/extlib/benz/error.c b/extlib/benz/error.c
index 08b1808e..b750a19a 100644
--- a/extlib/benz/error.c
+++ b/extlib/benz/error.c
@@ -4,6 +4,7 @@
 
 #include "picrin.h"
 #include "picrin/object.h"
+#include "picrin/state.h"
 
 void
 pic_panic(pic_state PIC_UNUSED(*pic), const char *msg)
@@ -98,6 +99,12 @@ pic_pop_handler(pic_state *pic)
   return pic_obj_value(*--pic->xp);
 }
 
+pic_value
+pic_err(pic_state *pic)
+{
+  return pic->err;
+}
+
 pic_value
 pic_make_error(pic_state *pic, const char *type, const char *msg, pic_value irrs)
 {
diff --git a/extlib/benz/eval.c b/extlib/benz/eval.c
index ace01513..02393339 100644
--- a/extlib/benz/eval.c
+++ b/extlib/benz/eval.c
@@ -5,6 +5,7 @@
 #include "picrin.h"
 #include "picrin/object.h"
 #include "picrin/opcode.h"
+#include "picrin/state.h"
 
 static pic_value
 optimize_beta(pic_state *pic, pic_value expr)
@@ -891,7 +892,7 @@ pic_eval(pic_state *pic, pic_value program, const char *lib)
   }
   pic_catch {
     pic_in_library(pic, prev_lib);
-    pic_raise(pic, pic->err);
+    pic_raise(pic, pic_err(pic));
   }
   pic_in_library(pic, prev_lib);
 
diff --git a/extlib/benz/file.c b/extlib/benz/file.c
index ac6f231b..bdb2e840 100644
--- a/extlib/benz/file.c
+++ b/extlib/benz/file.c
@@ -1,4 +1,9 @@
+/**
+ * See Copyright Notice in picrin.h
+ */
+
 #include "picrin.h"
+#include "picrin/state.h"
 
 #ifndef EOF
 # define EOF (-1)
diff --git a/extlib/benz/gc.c b/extlib/benz/gc.c
index d7813799..a7fe6338 100644
--- a/extlib/benz/gc.c
+++ b/extlib/benz/gc.c
@@ -4,6 +4,7 @@
 
 #include "picrin.h"
 #include "picrin/object.h"
+#include "picrin/state.h"
 
 enum {
   WHITE = 0,
diff --git a/extlib/benz/include/picrin.h b/extlib/benz/include/picrin.h
index 72c82833..0bfd26e2 100644
--- a/extlib/benz/include/picrin.h
+++ b/extlib/benz/include/picrin.h
@@ -98,7 +98,6 @@ void pic_export(pic_state *, pic_value sym);
 
 PIC_NORETURN void pic_panic(pic_state *, const char *msg);
 PIC_NORETURN void pic_errorf(pic_state *, const char *fmt, ...);
-PIC_NORETURN void pic_error(pic_state *, const char *type, const char *msg, pic_value irrs);
 PIC_NORETURN void pic_raise(pic_state *, pic_value v);
 
 pic_value pic_lambda(pic_state *, pic_func_t f, int n, ...);
@@ -296,8 +295,6 @@ int xvfprintf(pic_state *, xFILE *fp, const char *fmt, va_list);
 /* extra stuff */
 
 
-#include "picrin/state.h"
-
 void *pic_default_allocf(void *, void *, size_t);
 
 #define pic_assert_type(pic, v, type)                           \
@@ -355,6 +352,8 @@ void pic_exit_point(pic_state *);
 
 /* do not return from try block! */
 
+pic_value pic_err(pic_state *);
+
 #define pic_try                                 \
   pic_try_(PIC_GENSYM(cont), PIC_GENSYM(handler))
 #define pic_catch                               \
@@ -376,6 +375,8 @@ void pic_exit_point(pic_state *);
   if (0)                                                  \
   label:
 
+PIC_NORETURN void pic_error(pic_state *, const char *type, const char *msg, pic_value irrs);
+
 #define pic_for_each(var, list, it)                                     \
   for (it = (list); ! pic_nil_p(pic, it); it = pic_cdr(pic, it))        \
     if ((var = pic_car(pic, it)), true)
diff --git a/extlib/benz/include/picrin/object.h b/extlib/benz/include/picrin/object.h
index 397740d3..761d13f9 100644
--- a/extlib/benz/include/picrin/object.h
+++ b/extlib/benz/include/picrin/object.h
@@ -9,6 +9,8 @@
 extern "C" {
 #endif
 
+#include "picrin/khash.h"
+
 typedef struct pic_identifier pic_id;
 typedef pic_id pic_sym;
 
diff --git a/extlib/benz/lib.c b/extlib/benz/lib.c
index a7e9336a..63ea7a93 100644
--- a/extlib/benz/lib.c
+++ b/extlib/benz/lib.c
@@ -4,6 +4,7 @@
 
 #include "picrin.h"
 #include "picrin/object.h"
+#include "picrin/state.h"
 
 KHASH_DEFINE(ltable, const char *, struct pic_lib, kh_str_hash_func, kh_str_cmp_func)
 
diff --git a/extlib/benz/load.c b/extlib/benz/load.c
index 2ceefa11..7272c000 100644
--- a/extlib/benz/load.c
+++ b/extlib/benz/load.c
@@ -27,7 +27,7 @@ pic_load_cstr(pic_state *pic, const char *str)
   }
   pic_catch {
     pic_close_port(pic, port);
-    pic_raise(pic, pic->err);
+    pic_raise(pic, pic_err(pic));
   }
 
   pic_close_port(pic, port);
diff --git a/extlib/benz/macro.c b/extlib/benz/macro.c
index 6825aa62..2f8dc9cd 100644
--- a/extlib/benz/macro.c
+++ b/extlib/benz/macro.c
@@ -4,6 +4,7 @@
 
 #include "picrin.h"
 #include "picrin/object.h"
+#include "picrin/state.h"
 
 KHASH_DEFINE(env, pic_id *, pic_sym *, kh_ptr_hash_func, kh_ptr_hash_equal)
 
diff --git a/extlib/benz/port.c b/extlib/benz/port.c
index 6933c07a..af8a1f5b 100644
--- a/extlib/benz/port.c
+++ b/extlib/benz/port.c
@@ -4,6 +4,7 @@
 
 #include "picrin.h"
 #include "picrin/object.h"
+#include "picrin/file.h"
 
 #undef EOF
 #define EOF (-1)
diff --git a/extlib/benz/proc.c b/extlib/benz/proc.c
index 3a0c70ae..5182a6b5 100644
--- a/extlib/benz/proc.c
+++ b/extlib/benz/proc.c
@@ -5,6 +5,7 @@
 #include "picrin.h"
 #include "picrin/object.h"
 #include "picrin/opcode.h"
+#include "picrin/state.h"
 
 #define MIN(x,y) ((x) < (y) ? (x) : (y))
 
diff --git a/extlib/benz/read.c b/extlib/benz/read.c
index 86991f82..39404653 100644
--- a/extlib/benz/read.c
+++ b/extlib/benz/read.c
@@ -4,6 +4,7 @@
 
 #include "picrin.h"
 #include "picrin/object.h"
+#include "picrin/state.h"
 
 #undef EOF
 #define EOF (-1)
@@ -852,7 +853,7 @@ pic_read_cstr(pic_state *pic, const char *str)
   }
   pic_catch {
     pic_close_port(pic, port);
-    pic_raise(pic, pic->err);
+    pic_raise(pic, pic_err(pic));
   }
 
   pic_close_port(pic, port);
diff --git a/extlib/benz/state.c b/extlib/benz/state.c
index 58e35526..afd0c412 100644
--- a/extlib/benz/state.c
+++ b/extlib/benz/state.c
@@ -4,6 +4,7 @@
 
 #include "picrin.h"
 #include "picrin/object.h"
+#include "picrin/state.h"
 
 static void
 pic_init_features(pic_state *pic)
diff --git a/extlib/benz/symbol.c b/extlib/benz/symbol.c
index 20941f70..b073421e 100644
--- a/extlib/benz/symbol.c
+++ b/extlib/benz/symbol.c
@@ -4,6 +4,7 @@
 
 #include "picrin.h"
 #include "picrin/object.h"
+#include "picrin/state.h"
 
 #define kh_pic_str_hash(a) (pic_str_hash(pic, pic_obj_value(a)))
 #define kh_pic_str_cmp(a, b) (pic_str_cmp(pic, pic_obj_value(a), pic_obj_value(b)) == 0)
diff --git a/extlib/benz/var.c b/extlib/benz/var.c
index 6f59c0c7..df5ee003 100644
--- a/extlib/benz/var.c
+++ b/extlib/benz/var.c
@@ -4,6 +4,7 @@
 
 #include "picrin.h"
 #include "picrin/object.h"
+#include "picrin/state.h"
 
 static pic_value
 var_get(pic_state *pic, pic_value var)
diff --git a/extlib/benz/write.c b/extlib/benz/write.c
index 8d2276ed..d9822db3 100644
--- a/extlib/benz/write.c
+++ b/extlib/benz/write.c
@@ -4,6 +4,7 @@
 
 #include "picrin.h"
 #include "picrin/object.h"
+#include "picrin/state.h"
 
 KHASH_DECLARE(l, void *, int)
 KHASH_DECLARE(v, void *, int)