diff --git a/include/mruby/internal.h b/include/mruby/internal.h
index 96efc7697..ccfd30769 100644
--- a/include/mruby/internal.h
+++ b/include/mruby/internal.h
@@ -173,6 +173,12 @@ mrb_value mrb_f_send(mrb_state *mrb, mrb_value self);
 
 #ifdef MRB_USE_BIGINT
 mrb_value mrb_bint_new_int(mrb_state *mrb, mrb_int x);
+#ifdef MRB_INT64
+#define mrb_bint_new_int64(mrb,x) mrb_bint_new_int((mrb),(mrb_int)(x))
+#else
+mrb_value mrb_bint_new_int64(mrb_state *mrb, int64_t x);
+#endif
+mrb_value mrb_bint_new_uint64(mrb_state *mrb, uint64_t x);
 mrb_value mrb_bint_new_str(mrb_state *mrb, const char *x, mrb_int len, mrb_int base);
 mrb_value mrb_as_bint(mrb_state *mrb, mrb_value x);
 mrb_value mrb_bint_add(mrb_state *mrb, mrb_value x, mrb_value y);
diff --git a/mrbgems/mruby-bigint/core/bigint.c b/mrbgems/mruby-bigint/core/bigint.c
index a3457e275..cca54d31f 100644
--- a/mrbgems/mruby-bigint/core/bigint.c
+++ b/mrbgems/mruby-bigint/core/bigint.c
@@ -97,6 +97,39 @@ mpz_set_int(mrb_state *mrb, mpz_t *y, mrb_int v)
   }
 }
 
+static void
+mpz_set_uint64(mrb_state *mrb, mpz_t *y, uint64_t u)
+{
+  const size_t len = sizeof(uint64_t) / sizeof(mp_limb);
+
+  y->sn = (u != 0);
+  mpz_realloc(mrb, y, len);
+  for (size_t i=0; i<len; i++) {
+    y->p[i++] = (mp_limb)LOW(u);
+    u >>= DIG_SIZE;
+  }
+}
+
+#ifdef MRB_INT32
+static void
+mpz_set_int64(mrb_state *mrb, mpz_t *y, int64_t v)
+{
+  uint64_t u;
+
+  if (v < 0) {
+    if (v == INT64_MIN) u = v;
+    else u = -v;
+  }
+  else {
+    u = v;
+  }
+  mpz_set_uint64(mrb, y, u);
+  if (v < 0) {
+    y->sn = -1;
+  }
+}
+#endif
+
 static void
 mpz_init_set_int(mrb_state *mrb, mpz_t *y, mrb_int v)
 {
@@ -969,6 +1002,26 @@ mrb_bint_new_int(mrb_state *mrb, mrb_int x)
   return mrb_obj_value(b);
 }
 
+#ifdef MRB_INT32
+mrb_value
+mrb_bint_new_int64(mrb_state *mrb, int64_t x)
+{
+  struct RBigint *b = bint_new(mrb);
+  mpz_init(mrb, &b->mp);
+  mpz_set_int64(mrb, &b->mp, x);
+  return mrb_obj_value(b);
+}
+#endif
+
+mrb_value
+mrb_bint_new_uint64(mrb_state *mrb, uint64_t x)
+{
+  struct RBigint *b = bint_new(mrb);
+  mpz_init(mrb, &b->mp);
+  mpz_set_uint64(mrb, &b->mp, x);
+  return mrb_obj_value(b);
+}
+
 mrb_value
 mrb_bint_new_str(mrb_state *mrb, const char *x, mrb_int len, mrb_int base)
 {