diff --git a/channels/chan_sip.c b/channels/chan_sip.c
index a9d658b462..c9eefcdf8c 100644
--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -11082,10 +11082,23 @@ static int handle_request_subscribe(struct sip_pvt *p, struct sip_request *req,
  					p->subscribed = CPIM_PIDF_XML;    /* RFC 3863 format */
  				} else if (strstr(accept, "application/xpidf+xml")) {
  					p->subscribed = XPIDF_XML;        /* Early pre-RFC 3863 format with MSN additions (Microsoft Messenger) */
+				} else if (ast_strlen_zero(accept)) {
+					if (p->subscribed == NONE) { /* if the subscribed field is not already set, and there is no accept header... */
+						transmit_response(p, "489 Bad Event", req);
+
+						ast_log(LOG_WARNING,"SUBSCRIBE failure: no Accept header: pvt: stateid: %d, laststate: %d, dialogver: %d, subscribecont: '%s'\n",
+							p->stateid, p->laststate, p->dialogver, p->subscribecontext);
+						ast_set_flag(p, SIP_NEEDDESTROY);
+						return 0;
+					}
+					/* if p->subscribed is non-zero, then accept is not obligatory; according to rfc 3265 section 3.1.3, at least.
+					   so, we'll just let it ride, keeping the value from a previous subscription, and not abort the subscription */
 				} else {
  					/* Can't find a format for events that we know about */
- 					transmit_response(p, "489 Bad Event", req);
- 					ast_set_flag(p, SIP_NEEDDESTROY);	
+					char mybuf[200];
+					snprintf(mybuf,sizeof(mybuf),"489 Bad Event (format %s)", accept);
+ 					transmit_response(p, mybuf, req);
+ 					ast_set_flag(p, SIP_NEEDDESTROY);
  					return 0;
  				}
 				if (option_debug > 2)