diff --git a/cmake/configs/nuttx_px4fmu-v1_default.cmake b/cmake/configs/nuttx_px4fmu-v1_default.cmake
index 140df32fd84..f174ed46919 100644
--- a/cmake/configs/nuttx_px4fmu-v1_default.cmake
+++ b/cmake/configs/nuttx_px4fmu-v1_default.cmake
@@ -175,10 +175,12 @@ add_custom_target(sercon)
 set_target_properties(sercon PROPERTIES
 	PRIORITY "SCHED_PRIORITY_DEFAULT"
 	MAIN "sercon"
-	STACK_MAIN "2048")
+	STACK_MAIN "2048"
+	COMPILE_FLAGS "-Os")
 
 add_custom_target(serdis)
 set_target_properties(serdis PROPERTIES
 	PRIORITY "SCHED_PRIORITY_DEFAULT"
 	MAIN "serdis"
-	STACK_MAIN "2048")
+	STACK_MAIN "2048"
+	COMPILE_FLAGS "-Os")