diff --git a/nixos/lib/make-disk-image.nix b/nixos/lib/make-disk-image.nix
index 5e86ea479d5..feb6d194022 100644
--- a/nixos/lib/make-disk-image.nix
+++ b/nixos/lib/make-disk-image.nix
@@ -185,7 +185,8 @@ let format' = format; in let
       --system ${config.system.build.toplevel} --channel ${channelSources} --substituters ""
 
     echo "copying staging root to image..."
-    cptofs -p ${optionalString (partitionTableType != "none") "-P ${rootPartition}"} -t ${fsType} -i $diskImage $root/* /
+    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)
   '';
 in pkgs.vmTools.runInLinuxVM (
   pkgs.runCommand name