diff --git a/curses.h b/curses.h
index 33272f6b..2e9fcc42 100644
--- a/curses.h
+++ b/curses.h
@@ -46,8 +46,11 @@ PDCurses portable platform definitions list:
 # include <wchar.h>
 #endif
 
-#if defined(__STDC_VERSION__) && __STDC_VERSION >= 199901L && \
-    !defined(__bool_true_false_are_defined)
+#if defined(__STDC_VERSION__) && __STDC_VERSION >= 199901L
+# define PDC_99  1
+#endif
+
+#if defined(PDC_99) && !defined(__bool_true_false_are_defined)
 # include <stdbool.h>
 #endif
 
diff --git a/curspriv.h b/curspriv.h
index dbab0887..cbae8f7e 100644
--- a/curspriv.h
+++ b/curspriv.h
@@ -10,27 +10,18 @@
 #include <curses.h>
 
 #if defined(__TURBOC__) || defined(__EMX__) || defined(__DJGPP__) || \
-    defined(__CYGWIN__) || defined(__MINGW32__) || defined(__WATCOMC__)
+    defined(PDC_99) || defined(__WATCOMC__)
 # ifndef HAVE_VSSCANF
 #  define HAVE_VSSCANF       /* have vsscanf() */
 # endif
 #endif
 
-#if defined(__CYGWIN__) || defined(__MINGW32__) || defined(__WATCOMC__)
+#if defined(PDC_99) || defined(__WATCOMC__)
 # ifndef HAVE_VSNPRINTF
 #  define HAVE_VSNPRINTF     /* have vsnprintf() */
 # endif
 #endif
 
-#if defined(__STDC_VERSION__) && __STDC_VERSION >= 199901L
-# ifndef HAVE_VSSCANF
-#  define HAVE_VSSCANF
-# endif
-# ifndef HAVE_VSNPRINTF
-#  define HAVE_VSNPRINTF
-# endif
-#endif
-
 /*----------------------------------------------------------------------*/
 
 typedef struct           /* structure for ripped off lines */