diff --git a/Changes b/Changes
index e5e98c9..3d04563 100644
--- a/Changes
+++ b/Changes
@@ -1,7 +1,9 @@
 2.5 (Upcoming 2022)
 
-o -debug-force now properly documented as -decrypt-force
-o Switch to Yojson
+o New operation -impose for document imposition
+o New option -collate to collate page during merges
+o Option -debug-force now properly documented as -decrypt-force
+o Switch to Yojson for faster/better JSON input/output
 o Can read as well as write PDFs in JSON format with -j
 o Environment variable CPDF_REPRODUCIBLE_DATES for testing
 o Environment variable CPDF_DEBUG for -debug
diff --git a/cpdf.ml b/cpdf.ml
index 2dfd20b..5c92f55 100644
--- a/cpdf.ml
+++ b/cpdf.ml
@@ -2860,22 +2860,32 @@ let impose_pages n x y columns rtl btt center margin spacing linewidth mediabox'
 
 (* FIXME impose to use cropbox by default? See what happens with cropbox above. Clarify? Also point to hardbox. *)
 let impose ~x ~y ~fit ~columns ~rtl ~btt ~center ~margin ~spacing ~linewidth ~fast pdf =
-  Printf.printf
+  (*Printf.printf
     "impose: x = %f, y = %f, fit = %b, columns = %b, rtl = %b, btt = %b, center = %b, margin = %f, spacing = %f, linewidth = %f, fast = %b\n"
-    x y fit columns rtl btt center margin spacing linewidth fast;
-  let n = int_of_float x * int_of_float y in
+    x y fit columns rtl btt center margin spacing linewidth fast;*)
+  let endpage = Pdfpage.endpage pdf in
+  let ix = int_of_float x in
+  let iy = int_of_float y in
+  let n, ix, iy =
+      if ix = 0 && iy = 0 then error "impose-xy: both dimensions cannot be zero" else
+      if ix = 0 then (endpage, endpage, 1)
+      else if iy = 0 then (endpage, 1, endpage)
+      else (ix * iy, ix, iy)
+  in
   let firstpage = hd (Pdfpage.pages_of_pagetree pdf) in
   let mediabox' =
     if fit then Pdf.Array [Pdf.Real 0.; Pdf.Real 0.; Pdf.Real x; Pdf.Real y] else
       let _, _, w, h = Pdf.parse_rectangle firstpage.Pdfpage.mediabox in
-        Pdf.Array [Pdf.Real 0.; Pdf.Real 0.; Pdf.Real (w *. x); Pdf.Real (h *. y)]
+        if x = 0.0 then Pdf.Array [Pdf.Real 0.; Pdf.Real 0.; Pdf.Real (w *. float_of_int endpage); Pdf.Real h]
+        else if y = 0.0 then Pdf.Array [Pdf.Real 0.; Pdf.Real 0.; Pdf.Real w; Pdf.Real (h *. float_of_int endpage)]
+        else Pdf.Array [Pdf.Real 0.; Pdf.Real 0.; Pdf.Real (w *. x); Pdf.Real (h *. y)]
   in
-  let pagenums = ilist 1 (Pdfpage.endpage pdf) in
+  let pagenums = ilist 1 endpage in
   let pdf = upright pagenums pdf in
   let pages = Pdfpage.pages_of_pagetree pdf in
   let pagesets = splitinto n pages in
   let renumbered = map (Pdfpage.renumber_pages pdf) pagesets in
-  let pages' = map (impose_pages n x y columns rtl btt center margin spacing linewidth mediabox' fast pdf) renumbered in
+  let pages' = map (impose_pages n (float_of_int ix) (float_of_int iy) columns rtl btt center margin spacing linewidth mediabox' fast pdf) renumbered in
   let changes = map (fun x -> (x, (x + (n - 1)) / n)) pagenums in
     Pdfpage.change_pages ~changes true pdf pages'
 
diff --git a/cpdfcommand.ml b/cpdfcommand.ml
index 0b7f62e..2c264b7 100644
--- a/cpdfcommand.ml
+++ b/cpdfcommand.ml
@@ -4033,6 +4033,7 @@ let go () =
   | Some Impose fit ->
       let pdf = get_single_pdf args.op false in
       let x, y = Cpdfcoord.parse_coordinate pdf args.coord in
+        if not fit && (x < 0.0 || y < 0.0) then error "Negative imposition parameters not allowed." else
         write_pdf false
           (Cpdf.impose x y fit args.impose_columns args.impose_rtl args.impose_btt args.impose_center
                       args.impose_margin args.impose_spacing args.impose_linewidth args.fast pdf)
diff --git a/cpdfmanual.tex b/cpdfmanual.tex
index 1b92232..c167227 100644
--- a/cpdfmanual.tex
+++ b/cpdfmanual.tex
@@ -1,7 +1,7 @@
 %Document the new JSON format, -j and new -output-json options
 %Document -decrypt-force
 %Document -collate
-%Document -impose and friends
+%Document -impose and friends (inc. 0-w, 0-h for long ones)
 
 \documentclass{book}
 % Edit here to produce cpdfmanual.pdf, cpdflibmanual.pdf, pycpdfmanual.pdf etc.