diff --git a/mrblib/10error.rb b/mrblib/10error.rb
index 24ed68d4b..98d4d2a76 100644
--- a/mrblib/10error.rb
+++ b/mrblib/10error.rb
@@ -1,10 +1,3 @@
-class FloatDomainError < RangeError
-end
-
-# ISO 15.2.26
-class RegexpError < StandardError
-end
-
 # ISO 15.2.31
 class NameError < StandardError
   attr_accessor :name
diff --git a/src/error.c b/src/error.c
index 9d92ed8b0..1c7fa9370 100644
--- a/src/error.c
+++ b/src/error.c
@@ -710,7 +710,9 @@ mrb_init_exception(mrb_state *mrb)
   mrb->eStandardError_class = mrb_define_class_id(mrb, MRB_SYM(StandardError), mrb->eException_class); /* 15.2.23 */
   mrb_define_class_id(mrb, MRB_SYM(ArgumentError), E_STANDARD_ERROR);                                  /* 15.2.24 */
   mrb_define_class_id(mrb, MRB_SYM(LocalJumpError), E_STANDARD_ERROR);                                 /* 15.2.25 */
-  mrb_define_class_id(mrb, MRB_SYM(RangeError), E_STANDARD_ERROR);                                     /* 15.2.26 */
+  struct RClass *range_error = mrb_define_class_id(mrb, MRB_SYM(RangeError), E_STANDARD_ERROR);        /* 15.2.26 */
+  mrb_define_class_id(mrb, MRB_SYM(FloatDomainError), range_error);
+  mrb_define_class_id(mrb, MRB_SYM(RegexpError), E_STANDARD_ERROR);                                    /* 15.2.27 */
   struct RClass *runtime_error = mrb_define_class_id(mrb, MRB_SYM(RuntimeError), E_STANDARD_ERROR);    /* 15.2.28 */
   mrb_define_class_id(mrb, MRB_SYM(FrozenError), runtime_error);
   mrb_define_class_id(mrb, MRB_SYM(TypeError), E_STANDARD_ERROR);                                      /* 15.2.29 */