--- Mongoose/CMakeLists.txt.orig	2018-07-05 12:06:44.000000000 -0700
+++ Mongoose/CMakeLists.txt	2018-07-08 10:43:10.000000000 -0700
@@ -354,14 +354,14 @@
 message(STATUS "CMAKE_CXX_COMPILER: " ${BoldBlue} ${CMAKE_CXX_COMPILER_ID} ${ColourReset})
 if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang" OR "${CMAKE_CXX_COMPILER_ID}" STREQUAL "AppleClang")
     # using Clang
-    SET(CMAKE_CXX_FLAGS "-O3 -fwrapv")
+    SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fwrapv")
     # Debug flags for Clang
     SET(CMAKE_CXX_FLAGS_DEBUG "--coverage -g -fwrapv")
     SET(CMAKE_C_FLAGS_DEBUG "--coverage -g")
     SET(CMAKE_EXE_LINKER_FLAGS_DEBUG "--coverage -g")
 elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
     # using GCC
-    SET(CMAKE_CXX_FLAGS "-O3 -fwrapv")
+    SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fwrapv")
     # Debug flags for GCC
     if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS "4.6")
         set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x")
@@ -372,7 +372,7 @@
     SET(CMAKE_EXE_LINKER_FLAGS_DEBUG "-fprofile-arcs -ftest-coverage")
 elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Intel")
     # using Intel C++
-    SET(CMAKE_CXX_FLAGS "-O3 -no-prec-div -xHOST -ipo -fwrapv")
+    SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -no-prec-div -xHOST -ipo -fwrapv")
     # Debug flags for Intel
     SET(CMAKE_CXX_FLAGS_DEBUG "-g -O0 -Wall -fwrapv")
     SET(CMAKE_C_FLAGS_DEBUG "-g -O0 -Wall")