diff --git a/CMakeLists.txt b/CMakeLists.txt
index ba1f59094d54..538daabdc7e0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -243,6 +243,35 @@ if(NOT "${CMAKE_CXX_FLAGS}" STREQUAL "${COMPILER_FLAGS}")
 	)
 endif(NOT "${CMAKE_CXX_FLAGS}" STREQUAL "${COMPILER_FLAGS}")
 
+# #
+# Determine optimization level
+# #
+
+if(NOT OPT)
+	set(CMAKE_CXX_FLAGS_RELEASE "-O3")
+	set(CMAKE_C_FLAGS_RELEASE "-O3")
+
+	set(CMAKE_CXX_FLAGS_DEBUG "-O0")
+	set(CMAKE_C_FLAGS_DEBUG "-O0")
+
+	if(PROFILER STREQUAL "perf")
+		set(CMAKE_CXX_FLAGS_PROFILE "-Og")
+		set(CMAKE_C_FLAGS_PROFILE "-Og")
+	else(PROFILER STREQUAL "perf")
+		set(CMAKE_CXX_FLAGS_PROFILE "-O0")
+		set(CMAKE_C_FLAGS_PROFILE "-O0")
+	endif(PROFILER STREQUAL "perf")
+else(NOT OPT)
+	set(CMAKE_CXX_FLAGS_RELEASE "${OPT}")
+	set(CMAKE_C_FLAGS_RELEASE "${OPT}")
+
+	set(CMAKE_CXX_FLAGS_DEBUG "${OPT}")
+	set(CMAKE_C_FLAGS_DEBUG "${OPT}")
+
+	set(CMAKE_CXX_FLAGS_PROFILE "${OPT}")
+	set(CMAKE_C_FLAGS_PROFILE "${OPT}")
+endif(NOT OPT)
+
 # check for hardening options
 if(HARDEN AND NOT WIN32)
 	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fPIE -fstack-protector-strong")
@@ -254,7 +283,9 @@ if(HARDEN AND NOT WIN32)
 		set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -fPIE -pie -Wl,-z,relro,-z,now")
 	endif()
 
-	add_definitions(-D_FORTIFY_SOURCE=2)
+	if(NOT CMAKE_CXX_FLAGS_DEBUG STREQUAL "-O0")
+		add_definitions(-D_FORTIFY_SOURCE=2)
+	endif()
 endif(HARDEN AND NOT WIN32)
 
 if(UNIX AND NOT CMAKE_COMPILER_IS_GNUCXX)
@@ -282,35 +313,6 @@ RemoveFlag(CMAKE_C_FLAGS_MINSIZEREL CACHE "-DNDEBUG" "Default C flags for MinSiz
 RemoveFlag(CMAKE_SHARED_LIBRARY_LINK_CXX_FLAGS SCRIPT "-rdynamic" "")
 RemoveFlag(CMAKE_SHARED_LIBRARY_LINK_C_FLAGS SCRIPT "-rdynamic" "")
 
-# #
-# Determine optimization level
-# #
-
-if(NOT OPT)
-	set(CMAKE_CXX_FLAGS_RELEASE "-O3")
-	set(CMAKE_C_FLAGS_RELEASE "-O3")
-
-	set(CMAKE_CXX_FLAGS_DEBUG "-O0")
-	set(CMAKE_C_FLAGS_DEBUG "-O0")
-
-	if(PROFILER STREQUAL "perf")
-		set(CMAKE_CXX_FLAGS_PROFILE "-Og")
-		set(CMAKE_C_FLAGS_PROFILE "-Og")
-	else(PROFILER STREQUAL "perf")
-		set(CMAKE_CXX_FLAGS_PROFILE "-O0")
-		set(CMAKE_C_FLAGS_PROFILE "-O0")
-	endif(PROFILER STREQUAL "perf")
-else(NOT OPT)
-	set(CMAKE_CXX_FLAGS_RELEASE "${OPT}")
-	set(CMAKE_C_FLAGS_RELEASE "${OPT}")
-
-	set(CMAKE_CXX_FLAGS_DEBUG "${OPT}")
-	set(CMAKE_C_FLAGS_DEBUG "${OPT}")
-
-	set(CMAKE_CXX_FLAGS_PROFILE "${OPT}")
-	set(CMAKE_C_FLAGS_PROFILE "${OPT}")
-endif(NOT OPT)
-
 # #
 # Start determining options for Release build
 # #
diff --git a/SConstruct b/SConstruct
index 9900aa714e1b..f5998c7b4eac 100755
--- a/SConstruct
+++ b/SConstruct
@@ -506,7 +506,8 @@ for env in [test_env, client_env, env]:
 
         if env['harden'] and env["PLATFORM"] != 'win32':
             env.AppendUnique(CCFLAGS = ["-fPIE", "-fstack-protector-strong"])
-            if not env["have_fortify"] : env.AppendUnique(CPPDEFINES = ["_FORTIFY_SOURCE=2"])
+            if not env["have_fortify"] and "-O0" not in env["opt"]:
+                env.AppendUnique(CPPDEFINES = ["_FORTIFY_SOURCE=2"])
 
             if env["enable_lto"] == True:
                 env.AppendUnique(LINKFLAGS = ["-fstack-protector-strong"])