diff --git a/zconf.h b/zconf.h
index fd10c6a..84ffb32 100644
--- a/zconf.h
+++ b/zconf.h
@@ -266,11 +266,11 @@
 #  endif
 #endif
 
-#ifndef ON /* function prototypes for stdarg */
+#ifndef Z_ARG /* function prototypes for stdarg */
 #  if defined(STDC) || defined(Z_HAVE_STDARG_H)
-#    define ON(args)  args
+#    define Z_ARG(args)  args
 #  else
-#    define ON(args)  ()
+#    define Z_ARG(args)  ()
 #  endif
 #endif
 
diff --git a/zconf.h.cmakein b/zconf.h.cmakein
index 0b880ad..b2d78b3 100644
--- a/zconf.h.cmakein
+++ b/zconf.h.cmakein
@@ -268,11 +268,11 @@
 #  endif
 #endif
 
-#ifndef ON /* function prototypes for stdarg */
+#ifndef Z_ARG /* function prototypes for stdarg */
 #  if defined(STDC) || defined(Z_HAVE_STDARG_H)
-#    define ON(args)  args
+#    define Z_ARG(args)  args
 #  else
-#    define ON(args)  ()
+#    define Z_ARG(args)  ()
 #  endif
 #endif
 
diff --git a/zconf.h.in b/zconf.h.in
index fd10c6a..84ffb32 100644
--- a/zconf.h.in
+++ b/zconf.h.in
@@ -266,11 +266,11 @@
 #  endif
 #endif
 
-#ifndef ON /* function prototypes for stdarg */
+#ifndef Z_ARG /* function prototypes for stdarg */
 #  if defined(STDC) || defined(Z_HAVE_STDARG_H)
-#    define ON(args)  args
+#    define Z_ARG(args)  args
 #  else
-#    define ON(args)  ()
+#    define Z_ARG(args)  ()
 #  endif
 #endif
 
diff --git a/zlib.h b/zlib.h
index 6728d89..3121b0a 100644
--- a/zlib.h
+++ b/zlib.h
@@ -1298,7 +1298,7 @@ ZEXTERN int ZEXPORT gzwrite OF((gzFile file,
    error.
 */
 
-ZEXTERN int ZEXPORTVA gzprintf ON((gzFile file, const char *format, ...));
+ZEXTERN int ZEXPORTVA gzprintf Z_ARG((gzFile file, const char *format, ...));
 /*
      Converts, formats, and writes the arguments to the compressed file under
    control of the format string, as in fprintf.  gzprintf returns the number of