diff --git a/bts/BTS_Tests.ttcn b/bts/BTS_Tests.ttcn
index 1d3dfe7..3a3d7cc 100644
--- a/bts/BTS_Tests.ttcn
+++ b/bts/BTS_Tests.ttcn
@@ -917,6 +917,27 @@
 	}
 }
 
+/* This altstep triggers on receipt of a Downlink SACCH containing a L2 payload
+ * that matches the given LAPDm frame, as well as the given SACCH L1 header. */
+private altstep as_dl_sacch_lapdm_ab(out SacchL1Header l1h, out LapdmFrameAB frame,
+				     template (present) LapdmFrameAB tr_frame := ?,
+				     template (present) SacchL1Header tr_l1h := ?,
+			             template (present) GsmSapi sapi := ?)
+runs on ConnHdlr {
+	var L1ctlDlMessage dl_msg;
+	template (present) RslLinkId link_id := tr_RslLinkID_SACCH(sapi);
+	template (present) L1ctlDataReq tr_data := {
+		l1header := tr_l1h,
+		l2_payload := decmatch tr_frame
+	};
+
+	[] as_l1ctl_dl_msg(dl_msg, decmatch tr_data, g_chan_nr, link_id) {
+		var octetstring data := dl_msg.payload.data_ind.payload;
+		l1h := dec_SacchL1Header(substr(data, 0, 2));
+		frame := dec_LapdmFrameAB(substr(data, 2, lengthof(data) - 2));
+	}
+}
+
 /* This altstep is built on top of as_dl_dcch_lapdm_ab(), and triggers on receipt
  * of a LAPDm AB frame with a L3 payload matching the given template.  The L3
  * payload is treated as PDU_ML3_NW_MS. */