diff --git a/examples/25viewer.c b/examples/25viewer.c
index 37e4585..a0328f0 100644
--- a/examples/25viewer.c
+++ b/examples/25viewer.c
@@ -10,8 +10,9 @@
 
 static const char *fname; /* stores name of file to open */
 
-void quit()
+void quit(void *data)
 {
+   (void)data;
    exit(0);
 }