diff --git a/src/mk/localdefs.in b/src/mk/localdefs.in
index 0a97576d..48838425 100644
--- a/src/mk/localdefs.in
+++ b/src/mk/localdefs.in
@@ -33,5 +33,5 @@ LOCALCXXFLAGS = -g -O2 -Wall -Wno-unused \
 	      $(PICFLAGS) \
 	      @DEFS@
 
-CXXFLAGS = @CXXFLAGS@
+CXXFLAGS ?= @CXXFLAGS@