diff --git a/include/uchar.h b/include/uchar.h
index 5e10196d7..58cf1918f 100644
--- a/include/uchar.h
+++ b/include/uchar.h
@@ -30,12 +30,11 @@
 #define __need_mbstate_t
 #include <wchar.h>
 
-#ifndef __mbstate_t_defined
+#ifdef __mbstate_t_defined
 __BEGIN_NAMESPACE_C99
 /* Public type.  */
 typedef __mbstate_t mbstate_t;
 __END_NAMESPACE_C99
-# define __mbstate_t_defined 1
 #endif