-extern char *gnu_stpncpy (char *dst, const char *src, size_t n);
-#define stpncpy(Dst, Src, N) gnu_stpncpy (Dst, Src, N)
+#define stpncpy gnu_stpncpy
+
+/* Copy no more than N bytes of SRC to DST, returning a pointer past the
+ last non-NUL byte written into DST. */
+extern char *stpncpy (char *dst, const char *src, size_t n);