--- a/Makefile.in
+++ b/Makefile.in
@@ -477,7 +477,7 @@
 	./docs/style/lua-format -i scripts/*.nse
 
 makefile.dep:
-	$(CXX) -MM $(CPPFLAGS) $(SRCS) > $@
+	$(CXX) -MM $(CPPFLAGS) $(CXXFLAGS) $(SRCS) > $@
 -include makefile.dep
 
 # These the old names of scripts that have been renamed or deleted. Any