diff --git a/Include/unicodeobject.h b/Include/unicodeobject.h
index 01dce94..e88b8ed 100644
--- a/Include/unicodeobject.h
+++ b/Include/unicodeobject.h
@@ -78,7 +78,9 @@
    PyUnicode_AsWideChar(). */
 
 #ifdef HAVE_USABLE_WCHAR_T
-# define HAVE_WCHAR_H
+# ifndef HAVE_WCHAR_H
+#  define HAVE_WCHAR_H
+# endif
 #endif
 
 #ifdef HAVE_WCHAR_H