@@ -2369,7 +2369,7 @@ char * build_res_buf_from_sip_req( unsigned int code, str *text ,str *new_tag,

 			case HDR_TO_T:

 				if (new_tag && new_tag->len) {

 					to_tag=get_to(msg)->tag_value;

-					if ( to_tag.len || to_tag.s )

+					if ( to_tag.len && to_tag.s )

 						len+=new_tag->len-to_tag.len;

 					else

 						len+=new_tag->len+TOTAG_TOKEN_LEN/*";tag="*/;

@@ -2497,7 +2497,7 @@ char * build_res_buf_from_sip_req( unsigned int code, str *text ,str *new_tag,

 				break;

 			case HDR_TO_T:

 				if (new_tag && new_tag->len){

-					if (to_tag.s ) { /* replacement */

+					if (to_tag.len && to_tag.s) { /* replacement */

 						/* before to-tag */

 						append_str( p, hdr->name.s, to_tag.s-hdr->name.s);

 						/* to tag replacement */