diff --git a/CMakeLists.txt b/CMakeLists.txt
index 517ea33a..df320e43 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -997,9 +997,9 @@ if (CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_GNUCXX OR (CMAKE_C_COMPILER_ID
     endif()
 
     if (CMAKE_BUILD_TYPE MATCHES "DEBUG")
-	set(CMAKE_C_FLAGS "-O0" ${CMAKE_C_FLAGS})
+		set(CMAKE_C_FLAGS "-O0 ${CMAKE_C_FLAGS}")
     else()
-	set(CMAKE_C_FLAGS "-O3" ${CMAKE_C_FLAGS})
+		set(CMAKE_C_FLAGS "-O3 ${CMAKE_C_FLAGS}")
     endif()
 
     if (UNIX AND NOT LWS_WITH_ESP32)