diff --git a/Makefile b/Makefile
index 37677b7bf..a49d13cff 100644
--- a/Makefile
+++ b/Makefile
@@ -90,7 +90,7 @@ else ifeq ($(CXX), clang++)
 endif
 
 ifeq ($(HAVE_RULES),yes)
-    CXXFLAGS += -DHAVE_RULES -DTIXML_USE_STL $(shell pcre-config --cflags)
+    override CXXFLAGS += -DHAVE_RULES -DTIXML_USE_STL $(shell pcre-config --cflags)
     ifdef LIBS
         LIBS += $(shell pcre-config --libs)
     else
diff --git a/tools/dmake.cpp b/tools/dmake.cpp
index ca112f20b..696faad2a 100644
--- a/tools/dmake.cpp
+++ b/tools/dmake.cpp
@@ -363,7 +363,7 @@ int main(int argc, char **argv)
          << "\n";
 
     fout << "ifeq ($(HAVE_RULES),yes)\n"
-         << "    CXXFLAGS += -DHAVE_RULES -DTIXML_USE_STL $(shell pcre-config --cflags)\n"
+         << "    override CXXFLAGS += -DHAVE_RULES -DTIXML_USE_STL $(shell pcre-config --cflags)\n"
          << "    ifdef LIBS\n"
          << "        LIBS += $(shell pcre-config --libs)\n"
          << "    else\n"