--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -132,7 +132,7 @@ else(CMAKE_BUILD_TYPE STREQUAL Debug)
     if(MSVC)
         set(CMAKE_CXX_FLAGS "/O2")        ## Optimize
     else(MSVS)
-        set(CMAKE_CXX_FLAGS "-O3")
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
     endif()
 endif(CMAKE_BUILD_TYPE STREQUAL Debug)

@@ -147,7 +147,7 @@ endif()
 if(CMAKE_COMPILER_IS_GNUCXX)
     # issue #116 Library will not compile on CENTOS 7
     # set(CMAKE_EXE_LINKER_FLAGS "-static-libstdc++")
-    set(CMAKE_EXE_LINKER_FLAGS "-static-libgcc")
+    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -static-libgcc")
 endif()

 # from https://stackoverflow.com/questions/5395309/how-do-i-force-cmake-to-include-pthread-option-during-compilation