diff --git a/Makefile b/Makefile
index e26be920f68072bb552ab1c178c224d981e7b995..d3807e686161ab8d934dcfb290d9463e9135bef0 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 NAME_SRV = serial2-srv
 
-CXXFLAGS =
-LDFLAGS =
+CXXFLAGS +=
+LDFLAGS +=
 
 include ../makefiles/Make-9.3.3.in