--- d_ugen.c.org	2006-08-24 15:05:04.000000000 +0200
+++ d_ugen.c	2006-08-24 15:30:10.000000000 +0200
@@ -219,11 +219,11 @@
 
 static void block_bang(t_block *x)
 {
-    if (x->x_switched && !x->x_switchon)
+    if (dsp_chain && x->x_switched && !x->x_switchon)
     {
         t_int *ip;
         x->x_return = 1;
-        for (ip = dsp_chain + x->x_chainonset; ip; )
+        for (ip = dsp_chain + x->x_chainonset; ip&&*ip; )
             ip = (*(t_perfroutine)(*ip))(ip);
         x->x_return = 0;
     }
@@ -333,7 +333,7 @@
     if (dsp_chain)
     {
         t_int *ip;
-        for (ip = dsp_chain; ip; ) ip = (*(t_perfroutine)(*ip))(ip);
+        for (ip = dsp_chain; ip&&*ip; ) ip = (*(t_perfroutine)(*ip))(ip);
         dsp_phase++;
     }
 }