diff --git a/bts/BTS_Tests.ttcn b/bts/BTS_Tests.ttcn
index 909a331..8fc0fa9 100644
--- a/bts/BTS_Tests.ttcn
+++ b/bts/BTS_Tests.ttcn
@@ -2609,10 +2609,11 @@
 	/* Step 1: configure the RTP parameters */
 	var integer payload_len := 0;
 	var octetstring hdr := ''O;
+	var OCT1 pad := '00'O;
 
 	select (g_pars.chan_mode) {
 	case (tr_RSL_ChanMode(RSL_CHRT_TCH_F, RSL_CMOD_SP_GSM1)) /* TCH/FS */
-		{ payload_len := 33; hdr := 'D0'O; }
+		{ payload_len := 33; hdr := 'D0'O; pad := 'FF'O; }
 	case (tr_RSL_ChanMode(RSL_CHRT_TCH_H, RSL_CMOD_SP_GSM1)) /* TCH/HS */
 		{ payload_len := 15; hdr := '00'O; }
 	case (tr_RSL_ChanMode(RSL_CHRT_TCH_F, RSL_CMOD_SP_GSM2)) /* TCH/EFS */
@@ -2636,7 +2637,7 @@
 	}
 
 	/* Pad the payload to conform the expected length */
-	payload := f_pad_oct(hdr & payload, payload_len, '00'O);
+	payload := f_pad_oct(hdr & payload, payload_len, pad);
 	cfg.tx_payloads[0].fixed_payload := payload;
 	f_rtpem_configure(RTPEM_CTRL, cfg);