diff -u -r w2/tracker/Modules/Pro/effects.c work/tracker/Modules/Pro/effects.c
--- w2/tracker/Modules/Pro/effects.c	Sat Apr 13 19:16:54 1996
+++ work/tracker/Modules/Pro/effects.c	Sun Sep 27 19:44:20 1998
@@ -207,8 +207,9 @@
       /* temporary update of only the step value,
        * note that we do not change the saved pitch.
        */
-   set_temp_pitch(ch, 
-		ch->pitch + sinusoid_value(&(ch->vib))/256);
+	if (ch->pitch)
+		set_temp_pitch(ch, 
+			ch->pitch + sinusoid_value(&(ch->vib))/256);
    }
 
 LOCAL void set_vibrato(struct channel *ch, struct event *e)

