diff --git a/pkgs/development/tools/build-managers/redo-c/Makefile b/pkgs/development/tools/build-managers/redo-c/Makefile
index f2c43cc5003c..5a1dd74c5b84 100644
--- a/pkgs/development/tools/build-managers/redo-c/Makefile
+++ b/pkgs/development/tools/build-managers/redo-c/Makefile
@@ -1,4 +1,4 @@
-CFLAGS=-Os
+CFLAGS ?= -Os
 
 all: redo links