diff --git a/bts/BTS_Tests_LAPDm.ttcn b/bts/BTS_Tests_LAPDm.ttcn
index d6c605d..a5bcc56 100644
--- a/bts/BTS_Tests_LAPDm.ttcn
+++ b/bts/BTS_Tests_LAPDm.ttcn
@@ -3,12 +3,19 @@
 	import from Osmocom_Types all;
 	import from LAPDm_RAW_PT all;
 	import from LAPDm_Types all;
+	import from BTS_Tests all;
 
+	/* test that use exclusively only LAPDm over L1CTL */
 	type component lapdm_test_CT {
 		port LAPDm_PT LAPDM;
 		var lapdm_CT lapdm_component;
 	};
 
+	/* contrary to BTS_Tests.ttcn, we use LAPDm_PT here, a convenience wrapper
+	 * around L1CTL to perform encode/decode of abstract LAPDm frames */
+	type component lapdm_bts_CT extends lapdm_test_CT, test_CT {
+	}
+
 	function f_init() runs on lapdm_test_CT {
 		/* create the LAPDm component */
 		lapdm_component := lapdm_CT.create;