diff --git a/CMakeLists.txt b/CMakeLists.txt
index 567a815..d621647 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -170,6 +170,7 @@ target_compile_options(bootloader PUBLIC
   -Wmissing-format-attribute
   -Wno-endif-labels
   -Wunreachable-code
+  -Os
   # Suppress warning caused by SDK
   -Wno-unused-parameter -Wno-expansion-to-defined -Wno-array-bounds
   )
@@ -333,4 +334,4 @@ add_custom_target(flash-mbr
 
 add_custom_target(flash-erase
   COMMAND ${NRFJPROG} -f nrf52 --eraseall
-  )
\ No newline at end of file
+  )