diff --git a/Makefile b/Makefile
index 11f8fbe..7eee757 100644
--- a/Makefile
+++ b/Makefile
@@ -18,7 +18,7 @@ OCAMLLDFLAGS = -g
 all : native-code native-code-library byte-code-library top htdoc
 
 clean ::
-	rm -rf doc foo foo2 out.pdf out2.pdf foo.pdf *.cmt *.cmti *.json
+	rm -rf doc foo foo2 out.pdf out2.pdf foo.pdf *.cmt *.cmti *.json debug/*.pdf
 
 DOC_FILES = cpdferror.mli cpdfjson.mli cpdfstrftime.mli cpdfcoord.mli \
             cpdfattach.mli cpdfpagespec.mli cpdfposition.mli cpdf.mli \
diff --git a/cpdf.ml b/cpdf.ml
index 5142a84..45887f8 100644
--- a/cpdf.ml
+++ b/cpdf.ml
@@ -2977,14 +2977,17 @@ let twoup fast pdf =
         let endpage = Pdfpage.endpage pdf in
         let all = ilist 1 endpage in
         let pdf = scale_pdf ~fast (many (sc, sc) endpage) pdf all in
+        Pdfwrite.pdf_to_file pdf "scaled.pdf";
         let pdf =
           impose
             ~x:2. ~y:1. ~fit:false ~columns:false ~rtl:false ~btt:false ~center:true
             ~margin:0. ~spacing:0. ~linewidth:0. ~fast pdf
         in
+        Pdfwrite.pdf_to_file pdf "imposed.pdf";
         let endpage = Pdfpage.endpage pdf in
         let all = ilist 1 endpage in
         let pdf = upright all (rotate_pdf ~-90 pdf all) in
+          Pdfwrite.pdf_to_file pdf "uprighted.pdf";
           scale_to_fit_pdf ~fast Cpdfposition.Diagonal 1. (many (width, height) endpage) () pdf all
 
 (* \section{Output info} *)
diff --git a/debug/README.md b/debug/README.md
new file mode 100644
index 0000000..2dc005d
--- /dev/null
+++ b/debug/README.md
@@ -0,0 +1 @@
+For placing temporary debug PDF files. Cleaned by make clean.