diff --git a/include/wx/chartype.h b/include/wx/chartype.h
index 5162b91daf..a9e2dee892 100644
--- a/include/wx/chartype.h
+++ b/include/wx/chartype.h
@@ -154,8 +154,8 @@
     /* Sun's SunPro compiler supports the wchar_t type and wide character    */
     /* functions, but does not define __WCHAR_TYPE__. Define it here to      */
     /* allow unicode enabled builds.                                         */
-    #if defined(__SUNPRO_CC) || defined(__SUNPRO_C)
-    #define __WCHAR_TYPE__ wxchar_t
+    #if (defined(__SUNPRO_CC) || defined(__SUNPRO_C)) && !defined(__WCHAR_TYPE__)
+        #define __WCHAR_TYPE__ wxchar_t
     #endif
 
     /* GNU libc has __WCHAR_TYPE__ which requires special treatment, see */