diff --git a/nixos/lib/make-disk-image.nix b/nixos/lib/make-disk-image.nix
index feb6d194022..1cffca73563 100644
--- a/nixos/lib/make-disk-image.nix
+++ b/nixos/lib/make-disk-image.nix
@@ -186,7 +186,7 @@ let format' = format; in let
 
     echo "copying staging root to image..."
     cptofs -p ${optionalString (partitionTableType != "none") "-P ${rootPartition}"} -t ${fsType} -i $diskImage $root/* / ||
-      (echo "ERROR: cptofs failed. diskSize might be too small for closure."; exit 1)
+      (echo >&2 "ERROR: cptofs failed. diskSize might be too small for closure."; exit 1)
   '';
 in pkgs.vmTools.runInLinuxVM (
   pkgs.runCommand name