--- a/src/monitor/Makefile
+++ b/src/monitor/Makefile
@@ -36,7 +36,12 @@
 
 ifdef USE_SECURITY_FLAGS
 # Flags taken from: https://liquid.microsoft.com/Web/Object/Read/ms.security/Requirements/Microsoft.Security.SystemsADM.10203#guide
-SECURITY_CFLAGS=-fstack-protector-strong -D_FORTIFY_SOURCE=2 -O2 -z noexecstack -fpic -shared -Wl,-z,relro -Wl,-z,now -Wformat -Wformat-security -Werror=format-security
+SECURITY_CFLAGS=-fstack-protector-strong
+ifeq (,$(findstring _FORTIFY_SOURCE,$(CPPFLAGS)))
+	SECURITY_CFLAGS += -D_FORTIFY_SOURCE=2
+endif
+SECURITY_CFLAGS += -O2 -z noexecstack -fpic -shared -Wl,-z,relro -Wl,-z,now -Wformat -Wformat-security -Werror=format-security
+
 DEFAULT_CFLAGS += $(SECURITY_CFLAGS)
 endif
 
