diff --git a/src/lexer.mll b/src/lexer.mll
index 2f5836c36a5..b8aa9bbb8f5 100644
--- a/src/lexer.mll
+++ b/src/lexer.mll
@@ -22,23 +22,19 @@ let error_nest start lexbuf msg =
   lexbuf.Lexing.lex_start_p <- start;
   error lexbuf msg
 
-let classify_utf8_leader lexbuf = Int32.(function
-  | ch when logand ch (lognot 0b01111111l) = 0b00000000l -> 0
-  | ch when logand ch (lognot 0b00011111l) = 0b11000000l -> 1
-  | ch when logand ch (lognot 0b00001111l) = 0b11100000l -> 2
-  | ch when logand ch (lognot 0b00000111l) = 0b11110000l -> 3
-  | ch -> error lexbuf (Printf.sprintf "invalid utf-8 character: 0x%x" (Int32.to_int ch)))
-
-let utf8_decoder l lexbuf s i =
-  let leading = classify_utf8_leader lexbuf (Int32.of_int (Char.code s.[!i]))
-  in if leading = 0 then Char.code s.[!i]
-     else match Utf8.decode (String.sub s !i (1 + leading)) with
-          | [code] -> i := !i + leading; code
-          | _ -> error lexbuf "can not interpret unicode character"
-
-let unicode lexbuf s i decoder =
+
+let utf8 lexbuf s i =
+  let len =
+    if s.[!i] < '\x80' then 0 else
+    if s.[!i] < '\xe0' then 1 else
+    if s.[!i] < '\xf0' then 2 else 3
+  in
+  i := !i + len;
+  List.hd (Utf8.decode (String.sub s (!i - len) (1 + len)))
+
+let unicode lexbuf s i =
   let u =
-    if s.[!i] <> '\\' then decoder lexbuf s i else
+    if s.[!i] <> '\\' then utf8 lexbuf s i else
     match (incr i; s.[!i]) with
     | 'n' -> Char.code '\n'
     | 'r' -> Char.code '\r'
@@ -58,17 +54,14 @@ let unicode lexbuf s i decoder =
       int_of_string ("0x" ^ String.make 1 h ^ String.make 1 s.[!i])
   in incr i; u
 
-let char lexbuf s = unicode lexbuf s (ref 1) (fun _ _ _ ->
-                        match Utf8.decode s with
-                        | [39; code; 39] -> code (* surrounded by apostrophes *)
-                        | _ -> error lexbuf "can not interpret unicode character")
+let char lexbuf s =
+  unicode lexbuf s (ref 1)
 
 let text lexbuf s =
-  let l = String.length s in
-  let b = Buffer.create l in
+  let b = Buffer.create (String.length s) in
   let i = ref 1 in
-  while !i < l - 1 do
-    let bs = Utf8.encode [unicode lexbuf s i (utf8_decoder l)] in
+  while !i < String.length s - 1 do
+    let bs = Utf8.encode [unicode lexbuf s i] in
     Buffer.add_substring b bs 0 (String.length bs)
   done;
   Buffer.contents b