--- a/lib/linebuffer.h
+++ b/lib/linebuffer.h
@@ -25,18 +25,18 @@
 };
 
 #if defined (__STDC__) && __STDC__
-#define	_P(x) x
+#define	__P(x) x
 #else
-#define	_P(x) ()
+#define	__P(x) ()
 #endif
 
 /* Initialize linebuffer LINEBUFFER for use. */
-void initbuffer _P ((struct linebuffer *linebuffer));
+void initbuffer __P ((struct linebuffer *linebuffer));
 
 /* Read an arbitrarily long line of text from STREAM into LINEBUFFER.
    Remove any newline.  Does not null terminate.
    Return LINEBUFFER, except at end of file return 0.  */
-struct linebuffer *readline _P ((struct linebuffer *linebuffer, FILE *stream));
+struct linebuffer *readline __P ((struct linebuffer *linebuffer, FILE *stream));
 
 /* Free linebuffer LINEBUFFER and its data, all allocated with malloc. */
-void freebuffer _P ((struct linebuffer *));
+void freebuffer __P ((struct linebuffer *));