diff --git a/library/RAN_Emulation.ttcnpp b/library/RAN_Emulation.ttcnpp
index 543df2b..6a1f784 100644
--- a/library/RAN_Emulation.ttcnpp
+++ b/library/RAN_Emulation.ttcnpp
@@ -515,6 +515,9 @@
 		log("CommonBssmapUnitdataCallback: Not a paging message");
 	}
 	/* ELSE: handle in user callback */
+	if (not ispresent(g_ran_ops.unitdata_cb)) {
+		return omit;
+	}
 	return g_ran_ops.unitdata_cb.apply(bssap);
 }
 
@@ -675,6 +678,9 @@
 	}
 
 	/* ELSE: handle in user callback */
+	if (not ispresent(g_ran_ops.ranap_unitdata_cb)) {
+		return omit;
+	}
 	return g_ran_ops.ranap_unitdata_cb.apply(ranap);
 }