diff --git a/src/if_mzsch.c b/src/if_mzsch.c
index 39d1530..e4ebf29 100644
--- a/src/if_mzsch.c
+++ b/src/if_mzsch.c
@@ -886,19 +886,21 @@
     timer_id = 0;
 }
 
+#endif // MZSCHEME_GUI_THREADS
+
     char *
-did_set_mzquantum(void)
+did_set_mzquantum(optset_T *args UNUSED)
 {
+#if defined(MZSCHEME_GUI_THREADS)
     // reset timer
     if (timer_id != 0)
 	remove_timer();
     if (mz_threads_allow && p_mzq > 0 && gui.in_use)
 	setup_timer();
+#endif
     return NULL;
 }
 
-#endif // MZSCHEME_GUI_THREADS
-
     static void
 notify_multithread(int on)
 {