diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 0fc28da..81cd5af 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -19,7 +19,6 @@ jobs:
         - 4.05.0
         - 4.04.2
         - 4.03.0
-        - 4.02.3
 
     steps:
     - uses: actions/checkout@v2
diff --git a/Makefile b/Makefile
index 3f4c0c2..183a70b 100644
--- a/Makefile
+++ b/Makefile
@@ -97,8 +97,6 @@ package-docs : check-doc-prereqs docs
 
 .PHONY : check-doc-prereqs
 check-doc-prereqs :
-	@test $(OCAML_VERSION) -ne 402 \
-		|| (echo "\nocamldoc is broken in 4.02" && false)
 	@ocamlfind query lwt.unix > /dev/null 2> /dev/null \
 		|| (echo "\nLwt not installed" && false)
 	@ocamlfind query lambdasoup > /dev/null 2> /dev/null \
diff --git a/markup-lwt.opam b/markup-lwt.opam
index cf9b92e..21e5ac2 100644
--- a/markup-lwt.opam
+++ b/markup-lwt.opam
@@ -16,7 +16,7 @@ depends: [
   "dune" {>= "2.7.0"}
   "lwt"
   "markup"
-  "ocaml"
+  "ocaml" {>= "4.03.0"}
 ]
 
 build: [
diff --git a/markup.opam b/markup.opam
index d49407a..073f164 100644
--- a/markup.opam
+++ b/markup.opam
@@ -13,7 +13,7 @@ dev-repo: "git+https://github.com/aantron/markup.ml.git"
 
 depends: [
   "dune" {>= "2.7.0"}
-  "ocaml" {>= "4.02.0"}
+  "ocaml" {>= "4.03.0"}
   "uchar"
   "uutf" {>= "1.0.0"}
 
diff --git a/src/common.ml b/src/common.ml
index 9c12379..cbf60a4 100644
--- a/src/common.ml
+++ b/src/common.ml
@@ -1,19 +1,6 @@
 (* This file is part of Markup.ml, released under the MIT license. See
    LICENSE.md for details, or visit https://github.com/aantron/markup.ml. *)
 
-(* Aliases for reducing the number of deprecation warnings. *)
-module String =
-struct
-  include String
-  let lowercase = lowercase [@ocaml.warning "-3"]
-end
-
-module Char =
-struct
-  include Char
-  let lowercase = lowercase [@ocaml.warning "-3"]
-end
-
 type 'a cont = 'a -> unit
 type 'a cps = exn cont -> 'a cont -> unit
 
diff --git a/src/detect.ml b/src/detect.ml
index 383f407..9fe9fec 100644
--- a/src/detect.ml
+++ b/src/detect.ml
@@ -53,7 +53,7 @@ let guess_family_xml source throw k =
 
 (* 5.2 in the Encoding Candidate Recommendation. *)
 let normalize_name for_html s =
-  match String.lowercase (trim_string s) with
+  match String.lowercase_ascii (trim_string s) with
   | "unicode-1-1-utf-8" | "utf-8" | "utf8" ->
     "utf-8"
 
@@ -223,7 +223,7 @@ let meta_tag_prescan =
     let rec iterate () =
       next source throw (fun () -> k "") (function
         | c when c = quote -> k (Buffer.contents buffer)
-        | c -> add_utf_8 buffer (Char.code (Char.lowercase c)); iterate ())
+        | c -> add_utf_8 buffer (Char.code (Char.lowercase_ascii c)); iterate ())
     in
     iterate ()
   in
@@ -237,7 +237,7 @@ let meta_tag_prescan =
           push source c;
           k (Buffer.contents buffer)
         | c ->
-          add_utf_8 buffer (Char.code (Char.lowercase c));
+          add_utf_8 buffer (Char.code (Char.lowercase_ascii c));
           iterate ())
     in
     iterate ()
@@ -249,7 +249,7 @@ let meta_tag_prescan =
       next source throw (fun () -> k None) begin function
         | 'c' ->
           next_n 6 source throw begin fun l ->
-            match List.map Char.lowercase l with
+            match List.map Char.lowercase_ascii l with
             | ['h'; 'a'; 'r'; 's'; 'e'; 't'] ->
               skip_whitespace source throw (fun () ->
               next source throw (fun () -> k None) begin function
@@ -316,7 +316,7 @@ let meta_tag_prescan =
               k (Buffer.contents buffer)
 
             | Some c ->
-              add_utf_8 buffer (Char.code (Char.lowercase c));
+              add_utf_8 buffer (Char.code (Char.lowercase_ascii c));
               iterate ()
           end
         in
@@ -463,7 +463,7 @@ let meta_tag_prescan =
 
             | 'm' ->
               peek_n 5 source throw (fun l ->
-                match List.map Char.lowercase l with
+                match List.map Char.lowercase_ascii l with
                 | ['m'; 'e'; 't'; 'a'; c] when is_whitespace c || c = '/' ->
                   next_n 4 source throw (fun _ ->
                   process_meta_tag scan)
diff --git a/src/html_parser.ml b/src/html_parser.ml
index ed7c4b4..16dd3fd 100644
--- a/src/html_parser.ml
+++ b/src/html_parser.ml
@@ -240,7 +240,7 @@ struct
            Lowercase the element name given by the user before analysis by the
            parser, to match this convention. [String.lowercase] is acceptable
            here because the API assumes the string [element] is in UTF-8. *)
-        k (`Fragment (String.lowercase element), None)
+        k (`Fragment (String.lowercase_ascii element), None)
       | Some (`Document as c) -> k (c, None)
       | None -> detect tokens throw k)
     (fun (detected_context, deciding_token) ->
@@ -2825,7 +2825,7 @@ let parse requested_context report (tokens, set_tokenizer_state, set_foreign) =
     | l, `End {name} ->
       (fun mode' ->
         match Stack.current_element open_elements with
-        | Some {element_name = _, name'} when String.lowercase name' = name ->
+        | Some {element_name = _, name'} when String.lowercase_ascii name' = name ->
           mode' ()
         | _ ->
           report l (`Unmatched_end_tag name) !throw (fun () ->
@@ -2834,7 +2834,7 @@ let parse requested_context report (tokens, set_tokenizer_state, set_foreign) =
         let rec scan = function
           | [] -> mode ()
           | {element_name = ns, name'}::_
-              when String.lowercase name' = name ->
+              when String.lowercase_ascii name' = name ->
             close_element ~ns l name mode
           | {element_name = `HTML, _}::_ -> force_html ()
           | _::rest -> scan rest
diff --git a/src/markup.ml b/src/markup.ml
index 3a6dddc..04ba209 100644
--- a/src/markup.ml
+++ b/src/markup.ml
@@ -27,21 +27,11 @@ struct
     | None -> raise Not_synchronous
     | Some v -> v
 
-  (* Used in to_cps to avoid the need for a match .. with | exception ..
-     expression, which would break compatibility with OCaml < 4.02. Flambda
-     seems to optimizes the allocation of these results away completely. There
-     is a small performance penalty when not using Flambda. *)
-  type 'a result = Value of 'a | Exn of exn
-
   let to_cps f =
     fun throw k ->
-      let result =
-        try Value (f ())
-        with exn -> Exn exn
-      in
-      match result with
-      | Value v -> k v
-      | Exn exn -> throw exn
+      match f () with
+      | v -> k v
+      | exception exn -> throw exn
 end
 
 
diff --git a/src/stream_io.ml b/src/stream_io.ml
index e89f728..c83cb7b 100644
--- a/src/stream_io.ml
+++ b/src/stream_io.ml
@@ -1,7 +1,6 @@
 (* This file is part of Markup.ml, released under the MIT license. See
    LICENSE.md for details, or visit https://github.com/aantron/markup.ml. *)
 
-open Common
 open Kstream
 
 let state_fold f initial =
diff --git a/src/xml_tokenizer.ml b/src/xml_tokenizer.ml
index 298e0da..27d5b61 100644
--- a/src/xml_tokenizer.ml
+++ b/src/xml_tokenizer.ml
@@ -382,7 +382,7 @@ let tokenize report resolve_reference (input, get_location) =
     and target_state () =
       next' pi finish_pi begin function
         | _, c when is_whitespace c ->
-          if String.lowercase (Buffer.contents target_buffer) = "xml" then
+          if String.lowercase_ascii (Buffer.contents target_buffer) = "xml" then
             xml_declaration_state ()
           else
             text_state ()
@@ -422,7 +422,7 @@ let tokenize report resolve_reference (input, get_location) =
         report l (`Bad_token ("<?...", pi, "empty")) !throw (fun () ->
         k None)
       else
-        if String.lowercase (Buffer.contents target_buffer) = "xml" then
+        if String.lowercase_ascii (Buffer.contents target_buffer) = "xml" then
           finish_xml ()
         else
           k (Some
@@ -438,7 +438,7 @@ let tokenize report resolve_reference (input, get_location) =
         scan [] l
       in
 
-      let matches s (_, name, _) = String.lowercase name = s in
+      let matches s (_, name, _) = String.lowercase_ascii name = s in
 
       let version_valid s =
         String.length s = 3 &&
@@ -498,7 +498,7 @@ let tokenize report resolve_reference (input, get_location) =
               report l
                 (`Bad_token (value, xml, "must be 'yes' or 'no'")) !throw
                 (fun () ->
-              match String.lowercase value with
+              match String.lowercase_ascii value with
               | "yes" -> k (Some true)
               | "no" -> k (Some false)
               | _ -> k None))
diff --git a/test/test_detect.ml b/test/test_detect.ml
index 12094ac..80f4977 100644
--- a/test/test_detect.ml
+++ b/test/test_detect.ml
@@ -4,7 +4,6 @@
 open OUnit2
 open Test_support
 
-open Markup__Common
 open Markup__Kstream
 open Markup__Stream_io
 open Markup__Detect
diff --git a/test/test_utility.ml b/test/test_utility.ml
index 06198ae..d9c3a0f 100644
--- a/test/test_utility.ml
+++ b/test/test_utility.ml
@@ -4,7 +4,6 @@
 open OUnit2
 open Test_support
 
-open Markup__Common
 open! Markup
 module Kstream = Markup__Kstream