diff --git a/target/ep4ce6e22c/ice6809/ice6809.qsf b/target/ep4ce6e22c/ice6809/ice6809.qsf
index 517d101..504cdd7 100644
--- a/target/ep4ce6e22c/ice6809/ice6809.qsf
+++ b/target/ep4ce6e22c/ice6809/ice6809.qsf
@@ -112,6 +112,8 @@ set_global_assignment -name PARTITION_FITTER_PRESERVATION_LEVEL PLACEMENT_AND_RO
 set_global_assignment -name PARTITION_COLOR 16764057 -section_id Top
 set_instance_assignment -name PARTITION_HIERARCHY root_partition -to | -section_id Top
 
+set_global_assignment -name STRATIX_DEVICE_IO_STANDARD "3.3-V LVTTL"
+
 set_location_assignment PIN_24 -to clock
 set_location_assignment PIN_10 -to avr_TxD
 set_location_assignment PIN_23 -to avr_RxD