diff -ur asterisk-1.4.26.1/channels/chan_dahdi.c asterisk-1.4.26.1.new/channels/chan_dahdi.c
--- asterisk-1.4.26.1/channels/chan_dahdi.c	2009-09-23 10:36:03.000000000 +0300
+++ asterisk-1.4.26.1.new/channels/chan_dahdi.c	2009-09-23 10:37:41.000000000 +0300
@@ -2185,8 +2185,10 @@
 						struct dahdi_callerid cid;
 						
 						memset(&cid, 0, sizeof(cid));
-						strncpy(cid.cid_num, cid_num, DAHDI_MAX_CID - 1);
-						strncpy(cid.cid_name, cid_name, DAHDI_MAX_CID - 1);
+						if (cid_num)
+        						strncpy(cid.cid_num, cid_num, DAHDI_MAX_CID - 1);
+                                                if (cid_name)
+        						strncpy(cid.cid_name, cid_name, DAHDI_MAX_CID - 1);
 						ast_verbose("Sending CID IOCTL with %s %s\n", cid_num, cid_name);
 						if (ioctl(p->subs[SUB_REAL].dfd, DAHDI_SET_CALLERID, &cid))
 							ast_log(LOG_WARNING, "Unable to set caller-id info on '%s': %s\n", ast->name, strerror(errno));