diff --git a/include/mruby/internal.h b/include/mruby/internal.h
index 5083eed0b..4365b4f50 100644
--- a/include/mruby/internal.h
+++ b/include/mruby/internal.h
@@ -209,8 +209,8 @@ mrb_value mrb_bint_new_str(mrb_state *mrb, const char *x, mrb_int len, mrb_int b
 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);
 mrb_value mrb_bint_sub(mrb_state *mrb, mrb_value x, mrb_value y);
-mrb_value mrb_bint_add_d(mrb_state *mrb, mrb_value x, mrb_value y);
-mrb_value mrb_bint_sub_d(mrb_state *mrb, mrb_value x, mrb_value y);
+mrb_value mrb_bint_add_n(mrb_state *mrb, mrb_value x, mrb_value y);
+mrb_value mrb_bint_sub_n(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);
diff --git a/mrbgems/mruby-bigint/core/bigint.c b/mrbgems/mruby-bigint/core/bigint.c
index df2512113..ae3cc362b 100644
--- a/mrbgems/mruby-bigint/core/bigint.c
+++ b/mrbgems/mruby-bigint/core/bigint.c
@@ -1302,7 +1302,7 @@ mrb_bint_as_uint64(mrb_state *mrb, mrb_value x)
 
 /* unnormalize version of mrb_bint_add */
 mrb_value
-mrb_bint_add_d(mrb_state *mrb, mrb_value x, mrb_value y)
+mrb_bint_add_n(mrb_state *mrb, mrb_value x, mrb_value y)
 {
   y = mrb_as_bint(mrb, y);
   struct RBigint *b = RBIGINT(x);
@@ -1322,13 +1322,13 @@ mrb_bint_add(mrb_state *mrb, mrb_value x, mrb_value y)
     return mrb_float_value(mrb,v1+v2);
   }
 #endif
-  x = mrb_bint_add_d(mrb, x, y);
+  x = mrb_bint_add_n(mrb, x, y);
   return bint_norm(mrb, RBIGINT(x));
 }
 
 /* unnormalize version of mrb_bint_sub */
 mrb_value
-mrb_bint_sub_d(mrb_state *mrb, mrb_value x, mrb_value y)
+mrb_bint_sub_n(mrb_state *mrb, mrb_value x, mrb_value y)
 {
   y = mrb_as_bint(mrb, y);
   struct RBigint *b = RBIGINT(x);
@@ -1348,7 +1348,7 @@ mrb_bint_sub(mrb_state *mrb, mrb_value x, mrb_value y)
     return mrb_float_value(mrb,v1-v2);
   }
 #endif
-  x = mrb_bint_sub_d(mrb, x, y);
+  x = mrb_bint_sub_n(mrb, x, y);
   return bint_norm(mrb, RBIGINT(x));
 }
 
diff --git a/src/numeric.c b/src/numeric.c
index 50f27e913..a8979d2b6 100644
--- a/src/numeric.c
+++ b/src/numeric.c
@@ -1629,7 +1629,7 @@ int_truncate(mrb_state *mrb, mrb_value x)
 #ifdef MRB_USE_BIGINT
   if (mrb_bigint_p(x)) {
     mrb_value m = mrb_bint_mod(mrb, x, f);
-    x = mrb_bint_sub_d(mrb, x, m);
+    x = mrb_bint_sub_n(mrb, x, m);
     if (mrb_bint_cmp(mrb, x, mrb_fixnum_value(0)) < 0) {
       return mrb_bint_add(mrb, x, f);
     }