diff --git a/ChangeLog b/ChangeLog
index a61ff61c9f46ae..a1a8f14dd28393 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,26 @@
+Sat Jun 18 07:27:27 2011  Tanaka Akira  <akr@fsij.org>
+
+	* internal.h: declare internal functions here.
+
+	* node.h: declare NODE dependent internal functions here.
+
+	* iseq.h: declare rb_iseq_t dependent internal functions here.
+
+	* vm_core.h: declare rb_thread_t dependent internal functions here.
+
+	* bignum.c, class.c, compile.c, complex.c, cont.c, dir.c, encoding.c,
+	  enumerator.c, error.c, eval.c, file.c, gc.c, hash.c, inits.c, io.c,
+	  iseq.c, load.c, marshal.c, math.c, numeric.c, object.c, parse.y,
+	  proc.c, process.c, range.c, rational.c, re.c, ruby.c, string.c,
+	  thread.c, time.c, transcode.c, variable.c, vm.c,
+	  tool/compile_prelude.rb: don't declare internal functions declared
+	  in above headers.  include above headers if required.
+
+	  Note that rb_thread_mark() was declared as
+	  void rb_thread_mark(rb_thread_t *th) in cont.c but defined as
+	  void rb_thread_mark(void *ptr) in vm.c.  Now it is declared as
+	  the later in internal.h.
+
 Sat Jun 18 02:36:00 2011  Kenta Murata  <mrkn@mrkn.jp>
 
 	* ext/bigdecimal/bigdecimal.c (VpNewRbClass): fix type of the 2nd
diff --git a/bignum.c b/bignum.c
index b322a659ac75a7..809b164ff71dac 100644
--- a/bignum.c
+++ b/bignum.c
@@ -11,6 +11,7 @@
 
 #include "ruby/ruby.h"
 #include "ruby/util.h"
+#include "internal.h"
 
 #include <math.h>
 #include <float.h>
diff --git a/class.c b/class.c
index 828719c4ee0278..c6d011f2b61b97 100644
--- a/class.c
+++ b/class.c
@@ -120,8 +120,6 @@ rb_class_new(VALUE super)
     return rb_class_boot(super);
 }
 
-VALUE rb_iseq_clone(VALUE iseqval, VALUE newcbase);
-
 static void
 rb_mod_clone_method(VALUE klass, ID mid, const rb_method_entry_t *me)
 {
diff --git a/compile.c b/compile.c
index 6d596e6af2c246..b0e4514f4c87f2 100644
--- a/compile.c
+++ b/compile.c
@@ -10,6 +10,7 @@
 **********************************************************************/
 
 #include "ruby/ruby.h"
+#include "internal.h"
 #include <math.h>
 
 #define USE_INSN_STACK_INCREASE 1
@@ -155,7 +156,6 @@ r_value(VALUE value)
 #endif
 
 #if CPDEBUG > 1 || CPDEBUG < 0
-PRINTF_ARGS(void ruby_debug_printf(const char*, ...), 1, 2);
 #define debugs if (compile_debug_print_indent(1)) ruby_debug_printf
 #define debug_compile(msg, v) ((void)(compile_debug_print_indent(1) && fputs((msg), stderr)), (v))
 #else
diff --git a/complex.c b/complex.c
index decd996a91cfdc..7189e8bdf81a5e 100644
--- a/complex.c
+++ b/complex.c
@@ -6,6 +6,7 @@
 */
 
 #include "ruby.h"
+#include "internal.h"
 #include <math.h>
 
 #define NDEBUG
@@ -508,8 +509,6 @@ imp2(hypot)
 
 #define m_hypot(x,y) m_hypot_bang((x),(y))
 
-extern VALUE rb_math_log(int argc, VALUE *argv);
-
 static VALUE
 m_log_bang(VALUE x)
 {
@@ -1092,8 +1091,6 @@ nucomp_inexact_p(VALUE self)
 }
 #endif
 
-extern VALUE rb_lcm(VALUE x, VALUE y);
-
 /*
  * call-seq:
  *    cmp.denominator  ->  integer
diff --git a/cont.c b/cont.c
index 81bad6acee179b..f5e66987516113 100644
--- a/cont.c
+++ b/cont.c
@@ -10,6 +10,7 @@
 **********************************************************************/
 
 #include "ruby/ruby.h"
+#include "internal.h"
 #include "vm_core.h"
 #include "gc.h"
 #include "eval_intern.h"
@@ -126,7 +127,6 @@ static VALUE rb_eFiberError;
 
 NOINLINE(static VALUE cont_capture(volatile int *stat));
 
-void rb_thread_mark(rb_thread_t *th);
 #define THREAD_MUST_BE_RUNNING(th) do { \
 	if (!(th)->tag) rb_raise(rb_eThreadError, "not running thread");	\
     } while (0)
@@ -409,8 +409,6 @@ cont_new(VALUE klass)
     return cont;
 }
 
-void rb_vm_stack_to_heap(rb_thread_t *th);
-
 static VALUE
 cont_capture(volatile int *stat)
 {
diff --git a/dir.c b/dir.c
index 71df5dab98ad83..f8ad02d205ae40 100644
--- a/dir.c
+++ b/dir.c
@@ -13,6 +13,7 @@
 
 #include "ruby/ruby.h"
 #include "ruby/encoding.h"
+#include "internal.h"
 
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -1996,8 +1997,6 @@ file_s_fnmatch(int argc, VALUE *argv, VALUE obj)
     return Qfalse;
 }
 
-VALUE rb_home_dir(const char *user, VALUE result);
-
 /*
  *  call-seq:
  *    Dir.home()       -> "/home/me"
diff --git a/encoding.c b/encoding.c
index d152d77321a91d..95b2767911578b 100644
--- a/encoding.c
+++ b/encoding.c
@@ -11,6 +11,7 @@
 
 #include "ruby/ruby.h"
 #include "ruby/encoding.h"
+#include "internal.h"
 #include "regenc.h"
 #include <ctype.h>
 #ifndef NO_LOCALE_CHARMAP
diff --git a/enumerator.c b/enumerator.c
index 3f8d63286fbc7e..a1577ae5b022d9 100644
--- a/enumerator.c
+++ b/enumerator.c
@@ -1018,8 +1018,6 @@ generator_init(VALUE obj, VALUE proc)
     return obj;
 }
 
-VALUE rb_obj_is_proc(VALUE proc);
-
 /* :nodoc: */
 static VALUE
 generator_initialize(int argc, VALUE *argv, VALUE obj)
diff --git a/error.c b/error.c
index b89818337ee718..7c95455826dacb 100644
--- a/error.c
+++ b/error.c
@@ -12,6 +12,7 @@
 #include "ruby/ruby.h"
 #include "ruby/st.h"
 #include "ruby/encoding.h"
+#include "internal.h"
 #include "vm_core.h"
 
 #include <stdio.h>
@@ -230,8 +231,6 @@ rb_warn_m(VALUE self, VALUE mesg)
     return Qnil;
 }
 
-void rb_vm_bugreport(void);
-
 static void
 report_bug(const char *file, int line, const char *fmt, va_list args)
 {
diff --git a/eval.c b/eval.c
index 73b0a243f78fcc..87a1ac2e2caac7 100644
--- a/eval.c
+++ b/eval.c
@@ -16,6 +16,7 @@
 #include "gc.h"
 #include "ruby/vm.h"
 #include "ruby/encoding.h"
+#include "internal.h"
 #include "vm_core.h"
 
 #define numberof(array) (int)(sizeof(array) / sizeof((array)[0]))
@@ -35,12 +36,6 @@ VALUE rb_eSysStackError;
 
 /* initialize ruby */
 
-void rb_clear_trace_func(void);
-
-void rb_call_inits(void);
-void Init_heap(void);
-void Init_BareVM(void);
-
 void
 ruby_init(void)
 {
@@ -69,8 +64,6 @@ ruby_init(void)
     GET_VM()->running = 1;
 }
 
-extern void rb_clear_trace_func(void);
-
 void *
 ruby_options(int argc, char **argv)
 {
@@ -1053,9 +1046,6 @@ top_include(int argc, VALUE *argv, VALUE self)
     return rb_mod_include(argc, argv, rb_cObject);
 }
 
-VALUE rb_f_trace_var();
-VALUE rb_f_untrace_var();
-
 static VALUE *
 errinfo_place(rb_thread_t *th)
 {
diff --git a/file.c b/file.c
index d75398f3060942..bbe77d7a04c8c8 100644
--- a/file.c
+++ b/file.c
@@ -23,6 +23,7 @@
 #include "ruby/io.h"
 #include "ruby/util.h"
 #include "dln.h"
+#include "internal.h"
 
 #ifdef HAVE_UNISTD_H
 #include <unistd.h>
@@ -2203,8 +2204,6 @@ rb_file_s_lchown(int argc, VALUE *argv)
 #define rb_file_s_lchown rb_f_notimplement
 #endif
 
-struct timespec rb_time_timespec(VALUE time);
-
 struct utime_args {
     const struct timespec* tsp;
     VALUE atime, mtime;
@@ -5088,8 +5087,6 @@ is_explicit_relative(const char *path)
     return isdirsep(*path);
 }
 
-VALUE rb_get_load_path(void);
-
 static VALUE
 copy_path_class(VALUE path, VALUE orig)
 {
diff --git a/gc.c b/gc.c
index 137504ca7edc0c..d5b8dfd58f22e5 100644
--- a/gc.c
+++ b/gc.c
@@ -50,8 +50,6 @@
 # define VALGRIND_MAKE_MEM_UNDEFINED(p, n) /* empty */
 #endif
 
-int rb_io_fptr_finalize(struct rb_io_t*);
-
 #define rb_setjmp(env) RUBY_SETJMP(env)
 #define rb_jmp_buf rb_jmpbuf_t
 
@@ -2364,8 +2362,6 @@ obj_free(rb_objspace_t *objspace, VALUE obj)
 
 #define GC_NOTIFY 0
 
-void rb_vm_mark(void *ptr);
-
 #if STACK_GROW_DIRECTION < 0
 #define GET_STACK_BOUNDS(start, end, appendix) ((start) = STACK_END, (end) = STACK_START)
 #elif STACK_GROW_DIRECTION > 0
@@ -2406,8 +2402,6 @@ mark_current_machine_context(rb_objspace_t *objspace, rb_thread_t *th)
 #endif
 }
 
-void rb_gc_mark_encodings(void);
-
 static void
 gc_clear_mark_on_sweep_slots(rb_objspace_t *objspace)
 {
diff --git a/hash.c b/hash.c
index 742cbc62054c47..aa038a7147d247 100644
--- a/hash.c
+++ b/hash.c
@@ -690,8 +690,6 @@ rb_hash_default_proc(VALUE hash)
     return Qnil;
 }
 
-VALUE rb_obj_is_proc(VALUE proc);
-
 /*
  *  call-seq:
  *     hsh.default_proc = proc_obj     -> proc_obj
diff --git a/inits.c b/inits.c
index 6fb7463c57c3e8..73b9eb4283cf5d 100644
--- a/inits.c
+++ b/inits.c
@@ -10,6 +10,7 @@
 **********************************************************************/
 
 #include "ruby/ruby.h"
+#include "internal.h"
 
 #define CALL(n) {void Init_##n(void); Init_##n();}
 
diff --git a/internal.h b/internal.h
index bf1fcd5bb348f5..0bcfb7b8c48311 100644
--- a/internal.h
+++ b/internal.h
@@ -25,13 +25,128 @@ struct rb_classext_struct {
     struct st_table *const_tbl;
 };
 
+/* bignum.c */
+VALUE rb_big_fdiv(VALUE x, VALUE y);
 VALUE rb_big_uminus(VALUE x);
 
-VALUE rb_obj_is_thread(VALUE obj);
-VALUE rb_obj_is_mutex(VALUE obj);
+/* class.c */
+VALUE rb_obj_methods(int argc, VALUE *argv, VALUE obj);
+VALUE rb_obj_protected_methods(int argc, VALUE *argv, VALUE obj);
+VALUE rb_obj_private_methods(int argc, VALUE *argv, VALUE obj);
+VALUE rb_obj_public_methods(int argc, VALUE *argv, VALUE obj);
+
+/* compile.c */
+int rb_dvar_defined(ID);
+int rb_local_defined(ID);
+int rb_parse_in_eval(void);
+int rb_parse_in_main(void);
+
+/* debug.c */
+PRINTF_ARGS(void ruby_debug_printf(const char*, ...), 1, 2);
+
+/* dmyext.c */
+void Init_ext(void);
+
+/* encoding.c */
+ID rb_id_encoding(void);
+
+/* encoding.c */
+void rb_gc_mark_encodings(void);
+
+/* file.c */
+VALUE rb_home_dir(const char *user, VALUE result);
+VALUE rb_realpath_internal(VALUE basedir, VALUE path, int strict);
+void Init_File(void);
+
+/* gc.c */
+void Init_heap(void);
+
+/* inits.c */
+void rb_call_inits(void);
+
+/* io.c */
+const char *ruby_get_inplace_mode(void);
+void ruby_set_inplace_mode(const char *);
+int rb_io_fptr_finalize(struct rb_io_t*);
+ssize_t rb_io_bufwrite(VALUE io, const void *buf, size_t size);
+ssize_t rb_io_bufread(VALUE io, void *buf, size_t size);
+void rb_stdio_set_default_encoding(void);
+
+/* iseq.c */
+VALUE rb_iseq_compile_with_option(VALUE src, VALUE file, VALUE filepath, VALUE line, VALUE opt);
+VALUE rb_iseq_clone(VALUE iseqval, VALUE newcbase);
+
+/* load.c */
+VALUE rb_get_load_path(void);
+
+/* math.c */
+VALUE rb_math_log(int argc, VALUE *argv);
+
+/* newline.c */
+void Init_newline(void);
+
+/* numeric.c */
+VALUE rb_rational_reciprocal(VALUE x);
+int rb_num_to_uint(VALUE val, unsigned int *ret);
 
+/* parse.y */
+VALUE rb_parser_get_yydebug(VALUE);
+VALUE rb_parser_set_yydebug(VALUE, VALUE);
+
+/* rational.c */
+VALUE rb_lcm(VALUE x, VALUE y);
+
+/* re.c */
+VALUE rb_reg_compile(VALUE str, int options, const char *sourcefile, int sourceline);
+VALUE rb_reg_check_preprocess(VALUE);
+
+/* signal.c */
+int rb_get_next_signal(void);
+
+/* string.c */
+int rb_str_buf_cat_escaped_char(VALUE result, unsigned int c, int unicode_p);
+
+/* struct.c */
+VALUE rb_struct_init_copy(VALUE copy, VALUE s);
+
+/* time.c */
+struct timespec rb_time_timespec(VALUE time);
+struct timeval rb_time_timeval(VALUE);
+struct timeval rb_time_interval(VALUE);
+
+/* thread.c */
+VALUE rb_obj_is_mutex(VALUE obj);
+VALUE ruby_suppress_tracing(VALUE (*func)(VALUE, int), VALUE arg, int always);
 void rb_thread_execute_interrupts(VALUE th);
 void *rb_thread_call_with_gvl(void *(*func)(void *), void *data1);
+void rb_clear_trace_func(void);
+VALUE rb_thread_backtrace(VALUE thval);
+
+/* thread_pthread.c, thread_win32.c */
+void Init_native_thread(void);
+
+/* variable.c */
+VALUE rb_f_trace_var(int argc, VALUE *argv);
+VALUE rb_f_untrace_var(int argc, VALUE *argv);
+
+/* vm.c */
+VALUE rb_obj_is_thread(VALUE obj);
+void rb_vm_mark(void *ptr);
+void Init_BareVM(void);
+VALUE rb_vm_top_self(void);
+void rb_thread_recycle_stack_release(VALUE *);
+void rb_vm_change_state(void);
+void rb_vm_inc_const_missing_count(void);
+void rb_thread_mark(void *th);
+
+/* vm_dump.c */
+void rb_vm_bugreport(void);
+
+/* vm_eval.c */
+VALUE rb_funcall_passing_block(VALUE recv, ID mid, int argc, const VALUE *argv);
+
+/* miniprelude.c, prelude.c */
+void Init_prelude(void);
 
 #if defined(__cplusplus)
 #if 0
diff --git a/io.c b/io.c
index 657ffe41150d6f..9ce544c2ee42c5 100644
--- a/io.c
+++ b/io.c
@@ -82,8 +82,6 @@
 #include <sys/syscall.h>
 #endif
 
-extern void Init_File(void);
-
 #if defined(__BEOS__) || defined(__HAIKU__)
 # ifndef NOFILE
 #  define NOFILE (OPEN_MAX)
@@ -142,8 +140,6 @@ static ID id_write, id_read, id_getc, id_flush, id_readpartial, id_set_encoding;
 static VALUE sym_mode, sym_perm, sym_extenc, sym_intenc, sym_encoding, sym_open_args;
 static VALUE sym_textmode, sym_binmode, sym_autoclose;
 
-struct timeval rb_time_interval(VALUE);
-
 struct argf {
     VALUE filename, current_file;
     long last_lineno;		/* $. */
diff --git a/iseq.c b/iseq.c
index b821c602a3e390..25fc7929558d31 100644
--- a/iseq.c
+++ b/iseq.c
@@ -10,6 +10,7 @@
 **********************************************************************/
 
 #include "ruby/ruby.h"
+#include "internal.h"
 
 /* #define RUBY_MARK_FREE_DEBUG 1 */
 #include "gc.h"
@@ -217,8 +218,6 @@ set_relation(rb_iseq_t *iseq, const VALUE parent)
     }
 }
 
-VALUE rb_realpath_internal(VALUE basedir, VALUE path, int strict);
-
 static VALUE
 prepare_iseq_build(rb_iseq_t *iseq,
 		   VALUE name, VALUE filename, VALUE filepath, VALUE line_no,
diff --git a/iseq.h b/iseq.h
index d2aab1cc24541e..b626682bed34a9 100644
--- a/iseq.h
+++ b/iseq.h
@@ -24,6 +24,7 @@ VALUE rb_iseq_build_from_ary(rb_iseq_t *iseq, VALUE locals, VALUE args,
 
 /* iseq.c */
 VALUE rb_iseq_load(VALUE data, VALUE parent, VALUE opt);
+VALUE rb_iseq_parameters(const rb_iseq_t *iseq, int is_proc);
 struct st_table *ruby_insn_make_insn_table(void);
 
 struct rb_compile_option_struct {
diff --git a/load.c b/load.c
index 098772e92790b4..5d9d293273aa55 100644
--- a/load.c
+++ b/load.c
@@ -4,6 +4,7 @@
 
 #include "ruby/ruby.h"
 #include "ruby/util.h"
+#include "internal.h"
 #include "dln.h"
 #include "eval_intern.h"
 
@@ -267,7 +268,6 @@ rb_provide(const char *feature)
 }
 
 NORETURN(static void load_failed(VALUE));
-VALUE rb_realpath_internal(VALUE basedir, VALUE path, int strict);
 
 static void
 rb_load_internal(VALUE fname, int wrap)
diff --git a/marshal.c b/marshal.c
index 141288058b857f..557436894a0e6f 100644
--- a/marshal.c
+++ b/marshal.c
@@ -83,8 +83,6 @@ static ID s_dump, s_load, s_mdump, s_mload;
 static ID s_dump_data, s_load_data, s_alloc, s_call;
 static ID s_getbyte, s_read, s_write, s_binmode;
 
-ID rb_id_encoding(void);
-
 typedef struct {
     VALUE newclass;
     VALUE oldclass;
diff --git a/math.c b/math.c
index e3a78f74e3c510..7e073d7fe79a39 100644
--- a/math.c
+++ b/math.c
@@ -10,6 +10,7 @@
 **********************************************************************/
 
 #include "ruby/ruby.h"
+#include "internal.h"
 #include <math.h>
 #include <errno.h>
 
@@ -18,7 +19,6 @@
 VALUE rb_mMath;
 VALUE rb_eMathDomainError;
 
-extern VALUE rb_to_float(VALUE val);
 #define Need_Float(x) do {if (TYPE(x) != T_FLOAT) {(x) = rb_to_float(x);}} while(0)
 #define Need_Float2(x,y) do {\
     Need_Float(x);\
diff --git a/node.h b/node.h
index 9e922a4dbdec0b..bb96107711a2bb 100644
--- a/node.h
+++ b/node.h
@@ -457,6 +457,9 @@ VALUE rb_parser_end_seen_p(VALUE);
 VALUE rb_parser_encoding(VALUE);
 VALUE rb_parser_get_yydebug(VALUE);
 VALUE rb_parser_set_yydebug(VALUE, VALUE);
+VALUE rb_parser_dump_tree(NODE *node, int comment);
+NODE *rb_parser_append_print(VALUE, NODE *);
+NODE *rb_parser_while_loop(VALUE, NODE *, int, int);
 
 NODE *rb_parser_compile_cstr(volatile VALUE, const char*, const char*, int, int);
 NODE *rb_parser_compile_string(volatile VALUE, const char*, VALUE, int);
diff --git a/numeric.c b/numeric.c
index 1ec36ed7f87fdb..7a38404ab7dc15 100644
--- a/numeric.c
+++ b/numeric.c
@@ -2445,8 +2445,6 @@ fixdivmod(long x, long y, long *divp, long *modp)
     if (modp) *modp = mod;
 }
 
-VALUE rb_big_fdiv(VALUE x, VALUE y);
-
 /*
  *  call-seq:
  *     fix.fdiv(numeric)  ->  float
@@ -2475,8 +2473,6 @@ fix_fdiv(VALUE x, VALUE y)
     }
 }
 
-VALUE rb_rational_reciprocal(VALUE x);
-
 static VALUE
 fix_divide(VALUE x, VALUE y, ID op)
 {
diff --git a/object.c b/object.c
index 9cf925b7654af3..62edcb6c47421d 100644
--- a/object.c
+++ b/object.c
@@ -1838,11 +1838,6 @@ rb_mod_const_defined(int argc, VALUE *argv, VALUE mod)
     return RTEST(recur) ? rb_const_defined(mod, id) : rb_const_defined_at(mod, id);
 }
 
-VALUE rb_obj_methods(int argc, VALUE *argv, VALUE obj); /* in class.c */
-VALUE rb_obj_protected_methods(int argc, VALUE *argv, VALUE obj); /* in class.c */
-VALUE rb_obj_private_methods(int argc, VALUE *argv, VALUE obj); /* in class.c */
-VALUE rb_obj_public_methods(int argc, VALUE *argv, VALUE obj); /* in class.c */
-
 /*
  *  call-seq:
  *     obj.instance_variable_get(symbol)    -> obj
diff --git a/parse.y b/parse.y
index 60e5a3b8b12999..59e5d8d3f1e3be 100644
--- a/parse.y
+++ b/parse.y
@@ -18,6 +18,7 @@
 #include "ruby/ruby.h"
 #include "ruby/st.h"
 #include "ruby/encoding.h"
+#include "internal.h"
 #include "node.h"
 #include "parse.h"
 #include "id.h"
@@ -404,11 +405,6 @@ static ID  *local_tbl_gen(struct parser_params*);
 
 static void fixup_nodes(NODE **);
 
-extern int rb_dvar_defined(ID);
-extern int rb_local_defined(ID);
-extern int rb_parse_in_eval(void);
-extern int rb_parse_in_main(void);
-
 static VALUE reg_compile_gen(struct parser_params*, VALUE, int);
 #define reg_compile(str,options) reg_compile_gen(parser, (str), (options))
 static void reg_fragment_setenc_gen(struct parser_params*, VALUE, int);
@@ -5095,8 +5091,6 @@ parser_yyerror(struct parser_params *parser, const char *msg)
 static void parser_prepare(struct parser_params *parser);
 
 #ifndef RIPPER
-VALUE ruby_suppress_tracing(VALUE (*func)(VALUE, int), VALUE arg, int always);
-
 static VALUE
 debug_lines(const char *f)
 {
@@ -9213,9 +9207,6 @@ dvar_curr_gen(struct parser_params *parser, ID id)
 }
 
 #ifndef RIPPER
-VALUE rb_reg_compile(VALUE str, int options, const char *sourcefile, int sourceline);
-VALUE rb_reg_check_preprocess(VALUE);
-
 static void
 reg_fragment_setenc_gen(struct parser_params* parser, VALUE str, int options)
 {
diff --git a/proc.c b/proc.c
index f40e9daf10a129..7fae4f97edb20f 100644
--- a/proc.c
+++ b/proc.c
@@ -12,6 +12,7 @@
 #include "eval_intern.h"
 #include "internal.h"
 #include "gc.h"
+#include "iseq.h"
 
 struct METHOD {
     VALUE recv;
@@ -25,8 +26,6 @@ VALUE rb_cMethod;
 VALUE rb_cBinding;
 VALUE rb_cProc;
 
-VALUE rb_iseq_parameters(const rb_iseq_t *iseq, int is_proc);
-
 static VALUE bmcall(VALUE, VALUE);
 static int method_arity(VALUE);
 rb_iseq_t *rb_method_get_iseq(VALUE method);
diff --git a/process.c b/process.c
index d2592f55be4bde..7fdf31b0129548 100644
--- a/process.c
+++ b/process.c
@@ -14,6 +14,7 @@
 #include "ruby/ruby.h"
 #include "ruby/io.h"
 #include "ruby/util.h"
+#include "internal.h"
 #include "vm_core.h"
 
 #include <stdio.h>
@@ -39,8 +40,6 @@
 #define EXIT_FAILURE 1
 #endif
 
-struct timeval rb_time_interval(VALUE);
-
 #ifdef HAVE_SYS_WAIT_H
 # include <sys/wait.h>
 #endif
@@ -126,9 +125,6 @@ static VALUE rb_cProcessTms;
 	do {int saved_errno = errno; stmts; errno = saved_errno;} while (0)
 
 
-ssize_t rb_io_bufwrite(VALUE io, const void *buf, size_t size);
-ssize_t rb_io_bufread(VALUE io, void *buf, size_t size);
-
 /*
  *  call-seq:
  *     Process.pid   -> fixnum
diff --git a/range.c b/range.c
index 1866df150750e7..aa5472df062478 100644
--- a/range.c
+++ b/range.c
@@ -11,12 +11,11 @@
 
 #include "ruby/ruby.h"
 #include "ruby/encoding.h"
+#include "internal.h"
 
 VALUE rb_cRange;
 static ID id_cmp, id_succ, id_beg, id_end, id_excl;
 
-extern VALUE rb_struct_init_copy(VALUE copy, VALUE s);
-
 #define RANGE_BEG(r) (RSTRUCT(r)->as.ary[0])
 #define RANGE_END(r) (RSTRUCT(r)->as.ary[1])
 #define RANGE_EXCL(r) (RSTRUCT(r)->as.ary[2])
diff --git a/rational.c b/rational.c
index 00d71bf6417ba1..8dac978ca7aae0 100644
--- a/rational.c
+++ b/rational.c
@@ -6,6 +6,7 @@
 */
 
 #include "ruby.h"
+#include "internal.h"
 #include <math.h>
 #include <float.h>
 
diff --git a/re.c b/re.c
index ec3fd70b4accec..9fdbf547aaf33f 100644
--- a/re.c
+++ b/re.c
@@ -13,6 +13,7 @@
 #include "ruby/re.h"
 #include "ruby/encoding.h"
 #include "ruby/util.h"
+#include "internal.h"
 #include "regint.h"
 #include <ctype.h>
 
@@ -314,8 +315,6 @@ rb_reg_check(VALUE re)
     }
 }
 
-int rb_str_buf_cat_escaped_char(VALUE result, unsigned int c, int unicode_p);
-
 static void
 rb_reg_expr_str(VALUE str, const char *s, long len,
 	rb_encoding *enc, rb_encoding *resenc)
diff --git a/ruby.c b/ruby.c
index 4976ba185fe031..d93a908cc88698 100644
--- a/ruby.c
+++ b/ruby.c
@@ -17,6 +17,7 @@
 #endif
 #include "ruby/ruby.h"
 #include "ruby/encoding.h"
+#include "internal.h"
 #include "eval_intern.h"
 #include "dln.h"
 #include <stdio.h>
@@ -51,12 +52,6 @@
 char *getenv();
 #endif
 
-VALUE rb_parser_get_yydebug(VALUE);
-VALUE rb_parser_set_yydebug(VALUE, VALUE);
-
-const char *ruby_get_inplace_mode(void);
-void ruby_set_inplace_mode(const char *);
-
 #define DISABLE_BIT(bit) (1U << disable_##bit)
 enum disable_flag_bits {
     disable_gems,
@@ -377,7 +372,6 @@ ruby_init_loadpath_safe(int safe_level)
 #elif defined(HAVE_DLADDR)
     Dl_info dli;
     if (dladdr((void *)(VALUE)expand_include_path, &dli)) {
-	VALUE rb_realpath_internal(VALUE basedir, VALUE path, int strict);
 	char fbuf[MAXPATHLEN];
 	char *f = dln_find_file_r(dli.dli_fname, getenv(PATH_ENV), fbuf, sizeof(fbuf));
 	VALUE fname = rb_str_new_cstr(f ? f : dli.dli_fname);
@@ -477,9 +471,6 @@ add_modules(VALUE *req_list, const char *mod)
     rb_ary_push(list, rb_obj_freeze(rb_str_new2(mod)));
 }
 
-extern void Init_ext(void);
-extern VALUE rb_vm_top_self(void);
-
 static void
 require_libraries(VALUE *req_list)
 {
@@ -568,8 +559,6 @@ process_sflag(int *sflag)
     }
 }
 
-NODE *rb_parser_append_print(VALUE, NODE *);
-NODE *rb_parser_while_loop(VALUE, NODE *, int, int);
 static long proc_options(long argc, char **argv, struct cmdline_options *opt, int envopt);
 
 static void
@@ -1101,8 +1090,6 @@ proc_options(long argc, char **argv, struct cmdline_options *opt, int envopt)
     return argc0 - argc;
 }
 
-void Init_prelude(void);
-
 static void
 ruby_init_prelude(void)
 {
@@ -1237,10 +1224,6 @@ rb_f_chomp(argc, argv)
     return str;
 }
 
-void rb_stdio_set_default_encoding(void);
-VALUE rb_parser_dump_tree(NODE *node, int comment);
-VALUE rb_realpath_internal(VALUE basedir, VALUE path, int strict);
-
 static VALUE
 process_options(int argc, char **argv, struct cmdline_options *opt)
 {
diff --git a/string.c b/string.c
index 672245748618e7..9a85f8149375cb 100644
--- a/string.c
+++ b/string.c
@@ -14,6 +14,7 @@
 #include "ruby/ruby.h"
 #include "ruby/re.h"
 #include "ruby/encoding.h"
+#include "internal.h"
 #include <assert.h>
 
 #define BEG(no) (regs->beg[(no)])
@@ -2053,8 +2054,6 @@ rb_str_append(VALUE str, VALUE str2)
     return rb_str_buf_append(str, str2);
 }
 
-int rb_num_to_uint(VALUE val, unsigned int *ret);
-
 /*
  *  call-seq:
  *     str << integer       -> str
@@ -7459,8 +7458,6 @@ sym_to_sym(VALUE sym)
     return sym;
 }
 
-VALUE rb_funcall_passing_block(VALUE recv, ID mid, int argc, const VALUE *argv);
-
 static VALUE
 sym_call(VALUE args, VALUE sym, int argc, VALUE *argv)
 {
diff --git a/thread.c b/thread.c
index 34068b0300d7a1..4ea9f7e09c7a10 100644
--- a/thread.c
+++ b/thread.c
@@ -66,7 +66,6 @@ static void sleep_timeval(rb_thread_t *th, struct timeval time);
 static void sleep_wait_for_interrupt(rb_thread_t *th, double sleepsec);
 static void sleep_forever(rb_thread_t *th, int nodeadlock);
 static double timeofday(void);
-struct timeval rb_time_interval(VALUE);
 static int rb_threadptr_dead(rb_thread_t *th);
 
 static void rb_check_deadlock(rb_vm_t *vm);
@@ -409,7 +408,6 @@ thread_cleanup_func(void *th_ptr, int atfork)
 
 extern void ruby_error_print(void);
 static VALUE rb_threadptr_raise(rb_thread_t *, int, VALUE *);
-void rb_thread_recycle_stack_release(VALUE *);
 
 void
 ruby_thread_init_stack(rb_thread_t *th)
@@ -997,8 +995,6 @@ rb_thread_interrupted(VALUE thval)
     return RUBY_VM_INTERRUPTED(th);
 }
 
-struct timeval rb_time_timeval(VALUE);
-
 void
 rb_thread_sleep(int sec)
 {
@@ -2951,8 +2947,6 @@ rb_gc_save_machine_context(rb_thread_t *th)
  *
  */
 
-int rb_get_next_signal(void);
-
 void
 rb_threadptr_check_signal(rb_thread_t *mth)
 {
@@ -4024,7 +4018,6 @@ enum {
 };
 
 static VALUE thread_suppress_tracing(rb_thread_t *th, int ev, VALUE (*func)(VALUE, int), VALUE arg, int always);
-VALUE ruby_suppress_tracing(VALUE (*func)(VALUE, int), VALUE arg, int always);
 
 struct event_call_args {
     rb_thread_t *th;
@@ -4562,8 +4555,6 @@ thread_suppress_tracing(rb_thread_t *th, int ev, VALUE (*func)(VALUE, int), VALU
     return result;
 }
 
-VALUE rb_thread_backtrace(VALUE thval);
-
 /*
  *  call-seq:
  *     thr.backtrace    -> array
diff --git a/time.c b/time.c
index 20eea4728f6b46..0951e9a8a71281 100644
--- a/time.c
+++ b/time.c
@@ -14,6 +14,7 @@
 #include <time.h>
 #include <errno.h>
 #include "ruby/encoding.h"
+#include "internal.h"
 
 #ifdef HAVE_UNISTD_H
 #include <unistd.h>
diff --git a/tool/compile_prelude.rb b/tool/compile_prelude.rb
index 8ddf44edf13ec1..6ad9fce7daf5b6 100755
--- a/tool/compile_prelude.rb
+++ b/tool/compile_prelude.rb
@@ -83,6 +83,7 @@ def emit(outfile)
  sources: <%= @preludes.map {|n,*| prelude_base(n)}.join(', ') %>
 */
 #include "ruby/ruby.h"
+#include "internal.h"
 #include "vm_core.h"
 
 % preludes = @preludes.values.sort
@@ -115,8 +116,6 @@ def emit(outfile)
 % end
 
 % unless preludes.empty?
-VALUE rb_iseq_compile_with_option(VALUE src, VALUE file, VALUE filepath, VALUE line, VALUE opt);
-
 static void
 prelude_eval(VALUE code, VALUE name, VALUE line)
 {
diff --git a/transcode.c b/transcode.c
index 704c7404428b98..4d32cf705a488c 100644
--- a/transcode.c
+++ b/transcode.c
@@ -11,6 +11,7 @@
 
 #include "ruby/ruby.h"
 #include "ruby/encoding.h"
+#include "internal.h"
 #include "transcode_data.h"
 #include <ctype.h>
 
@@ -4299,8 +4300,6 @@ ecerr_incomplete_input(VALUE self)
     return rb_attr_get(self, rb_intern("incomplete_input"));
 }
 
-extern void Init_newline(void);
-
 /*
  *  Document-class: Encoding::UndefinedConversionError
  *
diff --git a/variable.c b/variable.c
index 6bd08c03905191..2de5eccf934c76 100644
--- a/variable.c
+++ b/variable.c
@@ -19,9 +19,6 @@
 #include "constant.h"
 #include "internal.h"
 
-void rb_vm_change_state(void);
-void rb_vm_inc_const_missing_count(void);
-
 st_table *rb_global_tbl;
 st_table *rb_class_tbl;
 static ID autoload, classpath, tmp_classpath, classid;
diff --git a/vm.c b/vm.c
index f6a21c8b839014..eacc6740e3a221 100644
--- a/vm.c
+++ b/vm.c
@@ -12,6 +12,7 @@
 #include "ruby/vm.h"
 #include "ruby/st.h"
 #include "ruby/encoding.h"
+#include "internal.h"
 
 #include "gc.h"
 #include "vm_core.h"
@@ -1662,8 +1663,6 @@ thread_recycle_struct(void)
 }
 #endif
 
-void rb_gc_mark_machine_stack(rb_thread_t *th);
-
 void
 rb_thread_mark(void *ptr)
 {
@@ -1866,8 +1865,6 @@ rb_thread_alloc(VALUE klass)
     return self;
 }
 
-VALUE rb_iseq_clone(VALUE iseqval, VALUE newcbase);
-
 static void
 vm_define_method(rb_thread_t *th, VALUE obj, ID id, VALUE iseqval,
 		 rb_num_t is_singleton, NODE *cref)
@@ -2151,9 +2148,6 @@ rb_vm_set_progname(VALUE filename)
 #if defined(ENABLE_VM_OBJSPACE) && ENABLE_VM_OBJSPACE
 struct rb_objspace *rb_objspace_alloc(void);
 #endif
-void ruby_thread_init_stack(rb_thread_t *th);
-
-extern void Init_native_thread(void);
 
 void
 Init_BareVM(void)
diff --git a/vm_core.h b/vm_core.h
index 98ec9b4c513f71..94025b953cd8cd 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -658,8 +658,11 @@ int rb_backtrace_each(rb_backtrace_iter_func *iter, void *arg);
 rb_control_frame_t *rb_vm_get_ruby_level_next_cfp(rb_thread_t *th, rb_control_frame_t *cfp);
 int rb_vm_get_sourceline(const rb_control_frame_t *);
 VALUE rb_name_err_mesg_new(VALUE obj, VALUE mesg, VALUE recv, VALUE method);
+void rb_vm_stack_to_heap(rb_thread_t *th);
+void ruby_thread_init_stack(rb_thread_t *th);
 
 NOINLINE(void rb_gc_save_machine_context(rb_thread_t *));
+void rb_gc_mark_machine_stack(rb_thread_t *th);
 
 #define sysstack_error GET_VM()->special_exceptions[ruby_error_sysstack]