--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -126,7 +126,7 @@ if (CMAKE_BUILD_TYPE STREQUAL Debug)
     endif()
 else(CMAKE_BUILD_TYPE STREQUAL Debug)
     if(CMAKE_COMPILER_IS_GNUCXX)
-        set(CMAKE_CXX_FLAGS "-O2 -fvisibility=internal")  ## Remove TlshImpl symbols
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fvisibility=internal")  ## Remove TlshImpl symbols
     endif()
     if(MSVC)
         set(CMAKE_CXX_FLAGS "/O2")        ## Optimize
@@ -142,8 +142,7 @@ endif()
 
 # user can override CXX; make sure tests link and load properly regardless of LD_LIBRARY_PATH
 if(CMAKE_COMPILER_IS_GNUCXX)
-    set(CMAKE_EXE_LINKER_FLAGS "-static-libgcc")
-    set(CMAKE_EXE_LINKER_FLAGS "-static-libstdc++")
+    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -static-libstdc++")
 endif()
 
 enable_testing()