diff --git a/CMakeLists.txt b/CMakeLists.txt
index 35b81fec6..c6c0758eb 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -193,7 +193,7 @@ endif()
 
 # Configuring compilers
 if(${CMAKE_CXX_COMPILER_ID} STREQUAL "Clang")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -pedantic -Wuninitialized -Wunreachable-code -Wstrict-overflow=2 -D_FORTIFY_SOURCE=2 -fPIC -fcolor-diagnostics")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -pedantic -Wuninitialized -Wunreachable-code -Wstrict-overflow=2 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fPIC -fcolor-diagnostics")
 elseif(${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU")
   set(COLOR_FLAG "-fdiagnostics-color=auto")
   check_cxx_compiler_flag("-fdiagnostics-color=auto" HAS_COLOR_FLAG)
@@ -201,7 +201,7 @@ elseif(${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU")
     set(COLOR_FLAG "")
   endif()
   # using GCC
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -pedantic -Wuninitialized -Wunreachable-code -Wstrict-overflow=1 -D_FORTIFY_SOURCE=2 ${COLOR_FLAG} -fPIC")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -pedantic -Wuninitialized -Wunreachable-code -Wstrict-overflow=1 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 ${COLOR_FLAG} -fPIC")
   if(WIN32) # using mingw
     add_dependency_defines(-DWIN32)
     set(OPTIONAL_SOCKET_LIBS ws2_32 wsock32)