diff --git a/include/mruby/bigint.h b/include/mruby/bigint.h
index 6dba4c7c9..925a5d27a 100644
--- a/include/mruby/bigint.h
+++ b/include/mruby/bigint.h
@@ -85,33 +85,6 @@ struct RBigint {
 
 #define RBIGINT(v) ((struct RBigint*)mrb_ptr(v))
 
-mrb_value mrb_bint_new_int(mrb_state *mrb, mrb_int x);
-mrb_value mrb_bint_add(mrb_state *mrb, mrb_value x, mrb_value y);
-mrb_value mrb_bint_sub(mrb_state *mrb, mrb_value x, mrb_value y);
-mrb_value mrb_bint_mul(mrb_state *mrb, mrb_value x, mrb_value y);
-mrb_value mrb_bint_div(mrb_state *mrb, mrb_value x, mrb_value y);
-mrb_value mrb_bint_divmod(mrb_state *mrb, mrb_value x, mrb_value y);
-mrb_value mrb_bint_add_ii(mrb_state *mrb, mrb_int x, mrb_int y);
-mrb_value mrb_bint_sub_ii(mrb_state *mrb, mrb_int x, mrb_int y);
-mrb_value mrb_bint_mul_ii(mrb_state *mrb, mrb_int x, mrb_int y);
-mrb_value mrb_bint_div_ii(mrb_state *mrb, mrb_int x, mrb_int y);
-mrb_value mrb_bint_mod(mrb_state *mrb, mrb_value x, mrb_value y);
-mrb_value mrb_bint_rem(mrb_state *mrb, mrb_value x, mrb_value y);
-mrb_value mrb_bint_pow(mrb_state *mrb, mrb_value x, mrb_value y);
-mrb_value mrb_bint_powm(mrb_state *mrb, mrb_value x, mrb_int y, mrb_value z);
-mrb_value mrb_bint_and(mrb_state *mrb, mrb_value x, mrb_value y);
-mrb_value mrb_bint_or(mrb_state *mrb, mrb_value x, mrb_value y);
-mrb_value mrb_bint_xor(mrb_state *mrb, mrb_value x, mrb_value y);
-mrb_value mrb_bint_rev(mrb_state *mrb, mrb_value x);
-mrb_value mrb_bint_lshift(mrb_state *mrb, mrb_value x, mrb_int width);
-mrb_value mrb_bint_rshift(mrb_state *mrb, mrb_value x, mrb_int width);
-mrb_value mrb_bint_to_s(mrb_state *mrb, mrb_value x, mrb_int base);
-#ifndef MRB_NO_FLOAT
-mrb_float mrb_bint_as_float(mrb_state *mrb, mrb_value x);
-#endif
-mrb_int mrb_bint_as_int(mrb_state *mrb, mrb_value x);
-mrb_int mrb_bint_cmp(mrb_state *mrb, mrb_value x, mrb_value y);
-void mrb_gc_free_bint(mrb_state *mrb, struct RBasic *x);
 #endif
 
 #endif  /* MRB_USE_BIGINT */