diff --git a/Changes b/Changes
index e9e89bc..3711fd1 100644
--- a/Changes
+++ b/Changes
@@ -1,7 +1,9 @@
 2.5 (Upcoming)
 
 o Environment variable CPDF_REPRODUCIBLE_DATES for testing
+o Environment variable CPDF_DEBUG for -debug
 o Effectively make stderr unbuffered
+o Prepend NOT to a page range to invert it
 
 2.4 (June 2021)
 
diff --git a/cpdf.ml b/cpdf.ml
index 2d87686..39f0202 100644
--- a/cpdf.ml
+++ b/cpdf.ml
@@ -435,38 +435,45 @@ let fixup_negatives endpage = function
       Pdfgenlex.LexInt (endpage + 1 + ~-(int_of_string (implode (tl (explode s)))))
   | x -> x
 
-let parse_pagespec_inner endpage pdf spec =
+let invert_range endpage r =
+  option_map (fun p -> if mem p r then None else Some p) (ilist 1 endpage)
+
+let rec parse_pagespec_inner endpage pdf spec =
   let spec = space_string spec in
     if endpage < 1 then raise (Pdf.PDFError "This PDF file has no pages and is therefore malformed") else
       let numbers =
         try
-          match rev (explode spec) with
-          | ['n'; 'e'; 'v'; 'e'] ->
-              keep even (ilist 1 endpage)
-          | ['d'; 'd'; 'o'] ->
-              keep odd (ilist 1 endpage)
-          | ['t'; 'i'; 'a'; 'r'; 't'; 'r'; 'o'; 'p'] ->
-              select_portrait pdf (ilist 1 endpage)
-          | ['e'; 'p'; 'a'; 'c'; 's'; 'd'; 'n'; 'a'; 'l'] ->
-              select_landscape pdf (ilist 1 endpage)
-          | 't'::'i'::'a'::'r'::'t'::'r'::'o'::'p'::more ->
-              select_portrait
-                pdf
-                (mk_numbers pdf endpage (map (fixup_negatives endpage) (Pdfgenlex.lex_string (implode (rev more)))))
-          | 'e'::'p'::'a'::'c'::'s'::'d'::'n'::'a'::'l'::more ->
-              select_landscape
-                pdf
-                (mk_numbers pdf endpage (map (fixup_negatives endpage) (Pdfgenlex.lex_string (implode (rev more)))))
-          | 'd'::'d'::'o'::more ->
-              keep
-                odd
-                (mk_numbers pdf endpage (map (fixup_negatives endpage) (Pdfgenlex.lex_string (implode (rev more)))))
-          | 'n'::'e'::'v'::'e'::more ->
-              keep
-                even
-                (mk_numbers pdf endpage (map (fixup_negatives endpage) (Pdfgenlex.lex_string (implode (rev more)))))
+          match explode spec with
+          | 'N'::'O'::'T'::r ->
+              invert_range endpage (parse_pagespec_inner endpage pdf (implode r))
           | _ ->
-              mk_numbers pdf endpage (map (fixup_negatives endpage) (Pdfgenlex.lex_string spec))
+            match rev (explode spec) with
+            | ['n'; 'e'; 'v'; 'e'] ->
+                keep even (ilist 1 endpage)
+            | ['d'; 'd'; 'o'] ->
+                keep odd (ilist 1 endpage)
+            | ['t'; 'i'; 'a'; 'r'; 't'; 'r'; 'o'; 'p'] ->
+                select_portrait pdf (ilist 1 endpage)
+            | ['e'; 'p'; 'a'; 'c'; 's'; 'd'; 'n'; 'a'; 'l'] ->
+                select_landscape pdf (ilist 1 endpage)
+            | 't'::'i'::'a'::'r'::'t'::'r'::'o'::'p'::more ->
+                select_portrait
+                  pdf
+                  (mk_numbers pdf endpage (map (fixup_negatives endpage) (Pdfgenlex.lex_string (implode (rev more)))))
+            | 'e'::'p'::'a'::'c'::'s'::'d'::'n'::'a'::'l'::more ->
+                select_landscape
+                  pdf
+                  (mk_numbers pdf endpage (map (fixup_negatives endpage) (Pdfgenlex.lex_string (implode (rev more)))))
+            | 'd'::'d'::'o'::more ->
+                keep
+                  odd
+                  (mk_numbers pdf endpage (map (fixup_negatives endpage) (Pdfgenlex.lex_string (implode (rev more)))))
+            | 'n'::'e'::'v'::'e'::more ->
+                keep
+                  even
+                  (mk_numbers pdf endpage (map (fixup_negatives endpage) (Pdfgenlex.lex_string (implode (rev more)))))
+            | _ ->
+                mk_numbers pdf endpage (map (fixup_negatives endpage) (Pdfgenlex.lex_string spec))
         with
           e -> raise PageSpecBadSyntax
       in
diff --git a/cpdfcommand.ml b/cpdfcommand.ml
index b12785b..a6d6786 100644
--- a/cpdfcommand.ml
+++ b/cpdfcommand.ml
@@ -4408,6 +4408,12 @@ let gs_malformed_force fi fo =
 ensure that all memory is cleaned. See clearance of filenames hashtable, for
 example. *)
 
+let process_env_vars () =
+  match Sys.getenv_opt "CPDF_DEBUG" with
+  | Some "true" -> args.debug <- true
+  | Some "false" -> args.debug <- false
+  | _ -> ()
+
 (* Main function. *)
 let go_withargv argv =
   (* Check for the standalone -gs-malformed-force special command line. This
@@ -4450,6 +4456,7 @@ let go_withargv argv =
            (*Printf.printf "AND:%b, %s\n" islast (Array.fold_left (fun x y -> x  ^ " " ^ y) "" s);
            flprint "\n";*)
            reset_arguments ();
+           process_env_vars ();
            parse_argv () s (align_specs specs) anon_fun usage_msg;
            parse_argv () (Array.of_list ("cpdf"::!control_args)) (align_specs specs) anon_fun usage_msg;
            let addrange pdf = AlreadyInMemory pdf, args.dashrange, "", "", ref false, None in
diff --git a/cpdfmanual.pdf b/cpdfmanual.pdf
index 18eed60..43d7f26 100644
Binary files a/cpdfmanual.pdf and b/cpdfmanual.pdf differ
diff --git a/cpdfmanual.tex b/cpdfmanual.tex
index 726b1bc..e67a6bd 100644
--- a/cpdfmanual.tex
+++ b/cpdfmanual.tex
@@ -459,6 +459,7 @@ at least five pages.
     \item The word \texttt{all} is the same as \texttt{1-end}.
     \item A range must contain no spaces.
     \item A tilde (\texttt{\~{}}) defines a page number counting from the end of the document rather than the beginning. Page \texttt{\~{}1} is the last page, \texttt{\~{}2} the penultimate page etc.
+    \item Prepending \texttt{NOT} to a whole page range inverts it.
   \end{itemize}
  
   \noindent For example: