diff --git a/src/pbs.cpp b/src/pbs.cpp
index 970b45cbda..1b97089b0f 100644
--- a/src/pbs.cpp
+++ b/src/pbs.cpp
@@ -1541,7 +1541,7 @@ void PBSWaitingPositionRestrictedSignalState::TraceRestrictExecuteResEndSlotIntl
 		TraceRestrictProgramResult out;
 		TraceRestrictProgramInput input(this->tile, this->trackdir, &VehiclePosTraceRestrictPreviousSignalCallback, nullptr);
 		input.permitted_slot_operations = TRPISP_PBS_RES_END_ACQUIRE;
-		if (tb_entrance_slots) input.permitted_slot_operations = TRPISP_ACQUIRE;
+		if (tb_entrance_slots) input.permitted_slot_operations |= TRPISP_ACQUIRE;
 		prog->Execute(v, input, out);
 	}
 }