diff -ur gsl-ocaml-1.19.1.old/myocamlbuild.ml gsl-ocaml-1.19.1/myocamlbuild.ml
--- gsl-ocaml-1.19.1.old/myocamlbuild.ml	2015-11-18 15:14:41.000000000 +0000
+++ gsl-ocaml-1.19.1/myocamlbuild.ml	2017-08-08 21:16:47.090002257 +0100
@@ -516,7 +516,7 @@
                  | nm, [], intf_modules ->
                      ocaml_lib nm;
                      let cmis =
-                       List.map (fun m -> (String.uncapitalize m) ^ ".cmi")
+                       List.map (fun m -> (String.uncapitalize_ascii m) ^ ".cmi")
                                 intf_modules in
                      dep ["ocaml"; "link"; "library"; "file:"^nm^".cma"] cmis
                  | nm, dir :: tl, intf_modules ->
@@ -529,7 +529,7 @@
                             ["compile"; "infer_interface"; "doc"])
                        tl;
                      let cmis =
-                       List.map (fun m -> dir^"/"^(String.uncapitalize m)^".cmi")
+                       List.map (fun m -> dir^"/"^(String.uncapitalize_ascii m)^".cmi")
                                 intf_modules in
                      dep ["ocaml"; "link"; "library"; "file:"^dir^"/"^nm^".cma"]
                          cmis)
diff -ur gsl-ocaml-1.19.1.old/setup.ml gsl-ocaml-1.19.1/setup.ml
--- gsl-ocaml-1.19.1.old/setup.ml	2015-11-18 15:14:41.000000000 +0000
+++ gsl-ocaml-1.19.1/setup.ml	2017-08-08 21:16:34.884995928 +0100
@@ -315,7 +315,7 @@
 
 
   let compare_csl s1 s2 =
-    String.compare (String.lowercase s1) (String.lowercase s2)
+    String.compare (String.lowercase_ascii s1) (String.lowercase_ascii s2)
 
 
   module HashStringCsl =
@@ -324,10 +324,10 @@
          type t = string
 
          let equal s1 s2 =
-             (String.lowercase s1) = (String.lowercase s2)
+             (String.lowercase_ascii s1) = (String.lowercase_ascii s2)
 
          let hash s =
-           Hashtbl.hash (String.lowercase s)
+           Hashtbl.hash (String.lowercase_ascii s)
        end)
 
   module SetStringCsl =
@@ -365,7 +365,7 @@
           else
             buf
         in
-          String.lowercase buf
+          String.lowercase_ascii buf
       end
 
 
@@ -471,7 +471,7 @@
         order     = Queue.create ();
         name_norm =
           (if case_insensitive then
-             String.lowercase
+             String.lowercase_ascii
            else
              fun s -> s);
       }
@@ -1822,13 +1822,13 @@
   let capitalize_file f =
     let dir = dirname f in
     let base = basename f in
-    concat dir (String.capitalize base)
+    concat dir (String.capitalize_ascii base)
 
 
   let uncapitalize_file f =
     let dir = dirname f in
     let base = basename f in
-    concat dir (String.uncapitalize base)
+    concat dir (String.uncapitalize_ascii base)
 
 
 end
@@ -5845,8 +5845,8 @@
     let make_fnames modul sufx =
       List.fold_right
         begin fun sufx accu ->
-          (String.capitalize modul ^ sufx) ::
-          (String.uncapitalize modul ^ sufx) ::
+          (String.capitalize_ascii modul ^ sufx) ::
+          (String.uncapitalize_ascii modul ^ sufx) ::
           accu
         end
         sufx