diff --git a/pkgs/tools/system/tree/default.nix b/pkgs/tools/system/tree/default.nix
index 0b19bd576874..78341e968184 100644
--- a/pkgs/tools/system/tree/default.nix
+++ b/pkgs/tools/system/tree/default.nix
@@ -30,7 +30,7 @@ stdenv.mkDerivation rec {
 
   preConfigure = ''
     sed -i Makefile -e 's|^OBJS=|OBJS=$(EXTRA_OBJS) |'
-    makeFlags+=("CC=$CC")
+    makeFlagsArray+=("CC=$CC")
   '';
 
   makeFlags = [