diff --git a/Meta/CMake/lagom_compile_options.cmake b/Meta/CMake/lagom_compile_options.cmake
index 7fec47ac843..64ddf53a379 100644
--- a/Meta/CMake/lagom_compile_options.cmake
+++ b/Meta/CMake/lagom_compile_options.cmake
@@ -29,9 +29,17 @@ if (CMAKE_BUILD_TYPE STREQUAL "Debug")
     if (NOT MSVC)
         add_cxx_compile_options(-ggdb3)
     endif()
-    add_cxx_compile_options(-Og)
+    if ("$ENV{CXXFLAGS}" MATCHES "(^| )(-O(fast|.?))( |$)")
+        add_cxx_compile_options(${CMAKE_MATCH_0})
+    else ()
+        add_cxx_compile_options(-Og)
+    endif()
 else()
-    add_cxx_compile_options(-O2)
+    if ("$ENV{CXXFLAGS}" MATCHES "(^| )(-O(fast|.?))( |$)")
+        add_cxx_compile_options(${CMAKE_MATCH_0})
+    else ()
+        add_cxx_compile_options(-O2)
+    endif()
     if (NOT MSVC)
         add_cxx_compile_options(-g1)
     endif()