diff --git a/thumbnails/Tupfile b/thumbnails/Tupfile
index 4aa8970..c866757 100644
--- a/thumbnails/Tupfile
+++ b/thumbnails/Tupfile
@@ -1 +1,7 @@
-run ./generate_thumbnails.tup
+: asset.raw |> !tup_preserve |>
+: asset.raw |> cp %f %o |> %B.thumbnail
+
+#: foreach *.raw |> !tup_preserve |>
+#: foreach *.raw |> cp %f %o |> %B.thumbnail
+
+#run ./generate_thumbnails.tup
diff --git a/thumbnails/preserve_bug.sh b/thumbnails/preserve_bug.sh
new file mode 100755
index 0000000..c43c389
--- /dev/null
+++ b/thumbnails/preserve_bug.sh
@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+
+tup # everything builds fine
+echo ""
+echo "Success"
+echo ""
+
+touch Tupfile
+
+tup # error
+echo ""
+echo "Fail"
+echo ""
+
+# tup error: Command ID 15 lists this file as both an input and an output:
+# build-default/asset.raw