diff --git a/CMakeLists.txt b/CMakeLists.txt
index fb20032..517218d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -29,8 +29,8 @@ set(CMAKE_LINKER /usr/bin/avr-ld)
 
 # Compiler flags
 add_definitions(-mmcu=${MCU} -DF_CPU=${CPU_SPEED})
-add_definitions(-s -c -g -O2 -Wall -std=c++17 )
-add_definitions(-fno-exceptions -ffunction-sections -fdata-sections)
+add_definitions(-s -c -g -Os -Wall -std=c++17 -flto)
+add_definitions(-fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics)
 
 # Linker flags
 set(CMAKE_SHARED_LIBRARY_LINK_C_FLAGS "-Os")   # remove -rdynamic for C