diff --git a/conf/firmwares/subsystems/fixedwing/ins_float_invariant.makefile b/conf/firmwares/subsystems/fixedwing/ins_float_invariant.makefile
index 4b4aa81190..34c7e22817 100644
--- a/conf/firmwares/subsystems/fixedwing/ins_float_invariant.makefile
+++ b/conf/firmwares/subsystems/fixedwing/ins_float_invariant.makefile
@@ -17,15 +17,8 @@ ifneq ($(AHRS_ALIGNER_LED),none)
   INS_CFLAGS += -DAHRS_ALIGNER_LED=$(AHRS_ALIGNER_LED)
 endif
 
-ifdef AHRS_PROPAGATE_FREQUENCY
-else
-  AHRS_PROPAGATE_FREQUENCY = 125
-endif
-
-ifdef AHRS_CORRECT_FREQUENCY
-else
-  AHRS_CORRECT_FREQUENCY = 125
-endif
+AHRS_PROPAGATE_FREQUENCY ?= 125
+AHRS_CORRECT_FREQUENCY ?= 125
 
 INS_CFLAGS += -DAHRS_PROPAGATE_FREQUENCY=$(AHRS_PROPAGATE_FREQUENCY)
 INS_CFLAGS += -DAHRS_CORRECT_FREQUENCY=$(AHRS_CORRECT_FREQUENCY)