--- a/Makefile.in
+++ b/Makefile.in
@@ -258,5 +258,5 @@
 	./config.status --recheck
 
 makefile.dep:
-	$(CXX) -MM $(CPPFLAGS) $(SRCS) > $@
+	$(CXX) -MM $(CPPFLAGS) $(CXXFLAGS) $(SRCS) > $@
 include makefile.dep