diff --git a/CMakeLists.txt b/CMakeLists.txt
index 722b07b973..e800ff643c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -16,7 +16,11 @@ endif()
 if(NOT BOOTLOADER_BUILD)
 
     if(CONFIG_COMPILER_OPTIMIZATION_SIZE)
-        list(APPEND compile_options "-Os")
+        if(CMAKE_C_COMPILER_ID MATCHES "Clang")
+            list(APPEND compile_options "-Oz")
+        else()
+            list(APPEND compile_options "-Os")
+        endif()
         if(CMAKE_C_COMPILER_ID MATCHES "GNU")
             list(APPEND compile_options "-freorder-blocks")
         endif()
@@ -34,7 +38,11 @@ if(NOT BOOTLOADER_BUILD)
 else()  # BOOTLOADER_BUILD
 
     if(CONFIG_BOOTLOADER_COMPILER_OPTIMIZATION_SIZE)
-        list(APPEND compile_options "-Os")
+        if(CMAKE_C_COMPILER_ID MATCHES "Clang")
+            list(APPEND compile_options "-Oz")
+        else()
+            list(APPEND compile_options "-Os")
+        endif()
         if(CMAKE_C_COMPILER_ID MATCHES "GNU")
             list(APPEND compile_options "-freorder-blocks")
         endif()