Index: ztcfg.c
===================================================================
--- ztcfg.c	(revision 2670)
+++ ztcfg.c	(working copy)
@@ -1398,6 +1398,7 @@
 						if (ioctl(fd, ZT_GET_PARAMS, &current_state))
 							needupdate = 1;
 						else if (current_state.chanpos == 16 &&
+							 (current_state.spanno - 1) < spans &&
 							(cc[x].sigtype & ZT_SIG_CLEAR) && 
 							!(lc[current_state.spanno - 1].lineconfig &
 							(ZT_CONFIG_D4|ZT_CONFIG_ESF|ZT_CONFIG_B8ZS|ZT_CONFIG_CCS))) {