--- plplot-5.12.0.old/examples/ocaml/x20.ml	2017-01-29 01:50:35.000000000 +0000
+++ plplot-5.12.0/examples/ocaml/x20.ml	2017-11-18 12:10:33.476409441 +0000
@@ -59,7 +59,7 @@
   let w, h = Scanf.sscanf w_h_line "%d %d" (fun w h -> w, h) in
   let num_col = Scanf.sscanf num_col_line "%d" (fun n -> n) in
 
-  let img = String.make (w * h) ' ' in
+  let img = Bytes.make (w * h) ' ' in
   let imf = Array.make_matrix w h 0.0 in
 
   (* Note that under 32bit OCaml, this will only work when reading strings up
@@ -72,7 +72,7 @@
     for j = 0 to h - 1 do
       imf.(i).(j) <-
         (* flip image up-down *)
-        float_of_int (int_of_char (img.[(h - 1 - j ) * w + i]));
+        float_of_int (int_of_char (Bytes.get img ((h - 1 - j ) * w + i)));
     done
   done;
   imf, w, h, num_col