diff --git a/make-freebsd.mk b/make-freebsd.mk
index 2a62c9f3d..b50efa813 100644
--- a/make-freebsd.mk
+++ b/make-freebsd.mk
@@ -34,7 +34,8 @@ else
 	STRIP=strip --strip-all
 endif
 
-CXXFLAGS=$(CFLAGS) -fno-rtti
+CXXFLAGS?=-fno-rtti
+CXXFLAGS=$(CFLAGS)
 
 all:	one
 
diff --git a/make-linux.mk b/make-linux.mk
index 949fc16d4..9719f36a2 100644
--- a/make-linux.mk
+++ b/make-linux.mk
@@ -40,7 +40,8 @@ endif
 #LDFLAGS=
 #STRIP=echo
 
-CXXFLAGS=$(CFLAGS) -fno-rtti
+CXXFLAGS?=-fno-rtti
+CXXFLAGS+=$(CFLAGS)
 
 all:	one
 
diff --git a/make-mac.mk b/make-mac.mk
index 8ea8b48c7..c9e05c5a4 100644
--- a/make-mac.mk
+++ b/make-mac.mk
@@ -38,7 +38,8 @@ else
 	STRIP=strip
 endif
 
-CXXFLAGS=$(CFLAGS) -fno-rtti
+CXXFLAGS?=-fno-rtti
+CXXFLAGS=$(CFLAGS)
 
 all: one