diff --git a/include/mruby.h b/include/mruby.h
index 8a0396753..2eff81245 100644
--- a/include/mruby.h
+++ b/include/mruby.h
@@ -1406,6 +1406,9 @@ MRB_API mrb_value mrb_check_string_type(mrb_state *mrb, mrb_value str);
 #define mrb_to_str(mrb, str) mrb_ensure_string_type(mrb,str)
 /* obsolete: use mrb_obj_as_string() instead */
 #define mrb_str_to_str(mrb, str) mrb_obj_as_string(mrb, str)
+/* check if val is an integer (including Bigint) */
+MRB_API mrb_value mrb_ensure_integer_type(mrb_state *mrb, mrb_value val);
+/* check if val fit in mrb_int */
 MRB_API mrb_value mrb_ensure_int_type(mrb_state *mrb, mrb_value val);
 #define mrb_as_int(mrb, val) mrb_integer(mrb_ensure_int_type(mrb, val))
 /* obsolete: use mrb_ensure_int_type() instead */
diff --git a/src/object.c b/src/object.c
index d03bfcfea..530702173 100644
--- a/src/object.c
+++ b/src/object.c
@@ -497,7 +497,7 @@ mrb_value mrb_complex_to_i(mrb_state *mrb, mrb_value comp);
 #endif
 
 MRB_API mrb_value
-mrb_ensure_int_type(mrb_state *mrb, mrb_value val)
+mrb_ensure_integer_type(mrb_state *mrb, mrb_value val)
 {
   if (!mrb_integer_p(val)) {
 #ifndef MRB_NO_FLOAT
@@ -506,6 +506,10 @@ mrb_ensure_int_type(mrb_state *mrb, mrb_value val)
     }
     else {
       switch (mrb_type(val)) {
+#ifdef MRB_USE_BIGINT
+      case MRB_TT_BIGINT:
+        return val;
+#endif
 #ifdef MRB_USE_RATIONAL
       case MRB_TT_RATIONAL:
         return mrb_rational_to_i(mrb, val);
@@ -524,6 +528,18 @@ mrb_ensure_int_type(mrb_state *mrb, mrb_value val)
   return val;
 }
 
+MRB_API mrb_value
+mrb_ensure_int_type(mrb_state *mrb, mrb_value val)
+{
+  val = mrb_ensure_integer_type(mrb, val);
+#ifdef MRB_USE_BIGINT
+  if (mrb_bigint_p(val)) {
+    return mrb_int_value(mrb, mrb_bint_as_int(mrb, val));
+  }
+#endif
+  return val;
+}
+
 #ifndef MRB_NO_FLOAT
 MRB_API mrb_value
 mrb_ensure_float_type(mrb_state *mrb, mrb_value val)