diff --git a/images/nix/default.nix b/images/nix/default.nix
index 4760758..78bf5fd 100644
--- a/images/nix/default.nix
+++ b/images/nix/default.nix
@@ -41,7 +41,7 @@ let
       ln -s ../bin usr/bin
 
       # make sure /tmp exists
-      mkdir -m 0777 tmp
+      mkdir -m 1777 tmp
     '';
 
     config = {