diff --git a/src/databits_callerid.c b/src/databits_callerid.c
index cfcc353..b1459ec 100644
--- a/src/databits_callerid.c
+++ b/src/databits_callerid.c
@@ -137,6 +137,8 @@ databits_decode_callerid( char *dataout_p, unsigned int dataout_size,
 	    cid_msgtype = CID_MSG_MDMF;
 	else if ( bits == CID_MSG_SDMF )
 	    cid_msgtype = CID_MSG_SDMF;
+	else
+	    return 0;
 	cid_buf[cid_ndata++] = bits;
 	return 0;
     }