diff --git a/py/builtintables.c b/py/builtintables.c
index 7b35207..5712a3e 100644
--- a/py/builtintables.c
+++ b/py/builtintables.c
@@ -123,7 +123,6 @@
     { MP_OBJ_NEW_QSTR(MP_QSTR_EOFError), (mp_obj_t)&mp_type_EOFError },
     { MP_OBJ_NEW_QSTR(MP_QSTR_Exception), (mp_obj_t)&mp_type_Exception },
     { MP_OBJ_NEW_QSTR(MP_QSTR_GeneratorExit), (mp_obj_t)&mp_type_GeneratorExit },
-    { MP_OBJ_NEW_QSTR(MP_QSTR_IOError), (mp_obj_t)&mp_type_IOError },
     { MP_OBJ_NEW_QSTR(MP_QSTR_ImportError), (mp_obj_t)&mp_type_ImportError },
     { MP_OBJ_NEW_QSTR(MP_QSTR_IndentationError), (mp_obj_t)&mp_type_IndentationError },
     { MP_OBJ_NEW_QSTR(MP_QSTR_IndexError), (mp_obj_t)&mp_type_IndexError },
diff --git a/py/obj.h b/py/obj.h
index d96e4ec..0156286 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -326,7 +326,6 @@
 extern const mp_obj_type_t mp_type_EOFError;
 extern const mp_obj_type_t mp_type_Exception;
 extern const mp_obj_type_t mp_type_GeneratorExit;
-extern const mp_obj_type_t mp_type_IOError;
 extern const mp_obj_type_t mp_type_ImportError;
 extern const mp_obj_type_t mp_type_IndentationError;
 extern const mp_obj_type_t mp_type_IndexError;
diff --git a/py/objexcept.c b/py/objexcept.c
index 7f07365..9b22acd 100644
--- a/py/objexcept.c
+++ b/py/objexcept.c
@@ -224,10 +224,10 @@
   MP_DEFINE_EXCEPTION(AssertionError, Exception)
   MP_DEFINE_EXCEPTION(AttributeError, Exception)
   //MP_DEFINE_EXCEPTION(BufferError, Exception)
-  //MP_DEFINE_EXCEPTION(EnvironmentError, Exception)
+  //MP_DEFINE_EXCEPTION(EnvironmentError, Exception) use OSError instead
   MP_DEFINE_EXCEPTION(EOFError, Exception)
   MP_DEFINE_EXCEPTION(ImportError, Exception)
-  MP_DEFINE_EXCEPTION(IOError, Exception)
+  //MP_DEFINE_EXCEPTION(IOError, Exception) use OSError instead
   MP_DEFINE_EXCEPTION(LookupError, Exception)
     MP_DEFINE_EXCEPTION_BASE(LookupError)
     MP_DEFINE_EXCEPTION(IndexError, LookupError)
diff --git a/py/qstrdefs.h b/py/qstrdefs.h
index fda140f..6a63f07 100644
--- a/py/qstrdefs.h
+++ b/py/qstrdefs.h
@@ -105,7 +105,6 @@
 Q(FileNotFoundError)
 Q(FloatingPointError)
 Q(GeneratorExit)
-Q(IOError)
 Q(ImportError)
 Q(IndentationError)
 Q(IndexError)