diff --git a/pkgs/build-support/docker/default.nix b/pkgs/build-support/docker/default.nix
index 35382662cf815e..ba76ce2b817da1 100644
--- a/pkgs/build-support/docker/default.nix
+++ b/pkgs/build-support/docker/default.nix
@@ -340,7 +340,7 @@ rec {
       # Tar up the layer and throw it into 'layer.tar'.
       echo "Packing layer..."
       mkdir $out
-      tarhash=$(tar -C layer --hard-dereference --sort=name --mtime="@$SOURCE_DATE_EPOCH" --owner=${toString uid} --group=${toString gid} -cf - . | tee $out/layer.tar | tarsum)
+      tarhash=$(tar -C layer --hard-dereference --sort=name --mtime="@$SOURCE_DATE_EPOCH" --owner=${toString uid} --group=${toString gid} -cf - . | tee -p $out/layer.tar | tarsum)
 
       # Add a 'checksum' field to the JSON, with the value set to the
       # checksum of the tarball.
@@ -425,7 +425,7 @@ rec {
         echo "Packing layer..."
         mkdir -p $out
         tarhash=$(tar -C layer --hard-dereference --sort=name --mtime="@$SOURCE_DATE_EPOCH" -cf - . |
-                    tee $out/layer.tar |
+                    tee -p $out/layer.tar |
                     ${tarsum}/bin/tarsum)
 
         cat ${baseJson} | jshon -s "$tarhash" -i checksum > $out/json