diff --git a/CHANGES.md b/CHANGES.md
index 4a97c9c..741ef72 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,6 +1,7 @@
 ## 8.1.2 (February 2022)
 * Add the `noargs` constructor for declaring interfaces that do not take any 
   parameters.
+* Allow Xmlrpc callers to override the base64 decoding function.
 
 ## 8.1.1 (November 2021)
 * Ignore error about using f-strings in python bindings (@psafont)
diff --git a/README.md b/README.md
index d57f95e..48be573 100644
--- a/README.md
+++ b/README.md
@@ -283,6 +283,46 @@ used to generate something from an interface defined following the above
 pattern. For example, it is possible to write an `RPC` implementation that
 generates a GUI for a given interface.
 
+## Base64 Decoding
+
+The treatment of line feeds (and other characters) in 
+[XML-RPC](http://xmlrpc.com) base64-encoded data is underspecified.
+
+By default, this library decodes values using the `Base64.decode_exn` 
+function of [ocaml-base64](https://github.com/mirage/ocaml-base64). This 
+function implements [RFC4648](https://datatracker.ietf.org/doc/html/rfc4648) 
+which requires the rejection of non-alphabet characters for security reasons 
+(see [section 3.3](https://datatracker.ietf.org/doc/html/rfc4648#section-3.3)
+and also [section 3.1](https://datatracker.ietf.org/doc/html/rfc4648#section-3.1)).
+
+This is problematic when communicating with servers that are less strict. 
+For instance, the 
+[encode](https://docs.python.org/3/library/xmlrpc.client.html#xmlrpc.client.Binary.encode) 
+function of the Python `xmlrpc.client` refers to [section 6.8 of 
+RFC2045](https://datatracker.ietf.org/doc/html/rfc2045.html#section-6.8) to 
+justify inserting a newline character every 76 characters.
+For this reasons, the functions in `Xmlrpc` allow the caller to override the 
+`base64_decoder`. The following declaration gives a rough-and-ready 
+“dangerous” implementation based on the `Base64.rfc2045` package.
+A better implementation would only accept a `\n` every 76 characters.
+
+```
+let base64_2045_decoder s =
+  let open Base64_rfc2045 in
+  let buf = Buffer.create 1024 in
+  let d = decoder (`String s) in
+  let rec go () =
+    match decode d with
+    | `Flush s -> (Buffer.add_string buf s; go ())
+    | `End -> Buffer.contents buf
+    (* best-effort *)
+    | `Malformed _   (* ignore missing '\r' before '\n', etc. *)
+    | `Wrong_padding (* ignore *)
+    | `Await -> go ()
+  in
+  go ()
+```
+
 ## Building
 
 To build, first install the dependencies:
diff --git a/src/lib/xmlrpc.ml b/src/lib/xmlrpc.ml
index 6167d73..ab8c470 100644
--- a/src/lib/xmlrpc.ml
+++ b/src/lib/xmlrpc.ml
@@ -313,13 +313,14 @@ module Parser = struct
   let make_float = make (fun data -> Float (float_of_string data))
   let make_string = make (fun data -> String data)
   let make_dateTime = make (fun data -> DateTime data)
-  let make_base64 = make (fun data -> Base64 (Base64.decode_exn data))
+  let make_base64 ?(base64_decoder=fun s -> Base64.decode_exn s) =
+    make (fun data -> Base64 (base64_decoder data))
   let make_enum = make (fun data -> Enum data)
   let make_dict = make (fun data -> Dict data)
 
   (* General parser functions *)
-  let rec of_xml ?callback accu input =
-    try value (map_tags (basic_types ?callback accu)) input with
+  let rec of_xml ?callback ?base64_decoder accu input =
+    try value (map_tags (basic_types ?callback ?base64_decoder accu)) input with
     | Xmlm.Error ((a, b), e) as exn ->
       eprintf "Characters %i--%i: %s\n%!" a b (Xmlm.error_message e);
       raise exn
@@ -328,13 +329,13 @@ module Parser = struct
       raise e
 
 
-  and basic_types ?callback accu input = function
+  and basic_types ?callback ?base64_decoder accu input = function
     | "int" | "i8" | "i4" -> make_int ?callback accu (get_data input)
     | "boolean" -> make_bool ?callback accu (get_data input)
     | "double" -> make_float ?callback accu (get_data input)
     | "string" -> make_string ?callback accu (get_data input)
     | "dateTime.iso8601" -> make_dateTime ?callback accu (get_data input)
-    | "base64" -> make_base64 ?callback accu (get_data input)
+    | "base64" -> make_base64 ?callback ?base64_decoder accu (get_data input)
     | "array" -> make_enum ?callback accu (data (of_xmls ?callback accu) input)
     | "struct" ->
       make_dict
@@ -359,25 +360,25 @@ module Parser = struct
     List.rev !r
 end
 
-let of_string ?callback str =
+let of_string ?callback ?base64_decoder str =
   let input = Xmlm.make_input (`String (0, str)) in
   (match Xmlm.peek input with
   | `Dtd _ -> ignore (Xmlm.input input)
   | _ -> ());
-  Parser.of_xml ?callback [] input
+  Parser.of_xml ?callback ?base64_decoder [] input
 
 
-let of_a ?callback ~next_char b =
+let of_a ?callback ?base64_decoder ~next_char b =
   let aux () =
     match next_char b with
     | Some c -> int_of_char c
     | None -> raise End_of_file
   in
   let input = Xmlm.make_input (`Fun aux) in
-  Parser.of_xml ?callback [] input
+  Parser.of_xml ?callback ?base64_decoder [] input
 
 
-let call_of_string ?callback str =
+let call_of_string ?callback ?base64_decoder str =
   let input = Xmlm.make_input (`String (0, str)) in
   (match Xmlm.peek input with
   | `Dtd _ -> ignore (Xmlm.input input)
@@ -395,7 +396,8 @@ let call_of_string ?callback str =
           while Xmlm.peek input <> `El_end do
             Parser.map_tag
               "param"
-              (fun input -> params := Parser.of_xml ?callback [] input :: !params)
+              (fun input -> params :=
+                Parser.of_xml ?callback ?base64_decoder [] input :: !params)
               input;
             Parser.skip_empty input
           done)
@@ -404,11 +406,11 @@ let call_of_string ?callback str =
   call !name (List.rev !params)
 
 
-let response_of_fault ?callback input =
+let response_of_fault ?callback ?base64_decoder input =
   Parser.map_tag
     "fault"
     (fun input ->
-      match Parser.of_xml ?callback [] input with
+      match Parser.of_xml ?callback ?base64_decoder [] input with
       | Dict d ->
         let fault_code = List.assoc "faultCode" d in
         let fault_string = List.assoc "faultString" d in
@@ -417,14 +419,14 @@ let response_of_fault ?callback input =
     input
 
 
-let response_of_success ?callback input =
+let response_of_success ?callback ?base64_decoder input =
   Parser.map_tag
     "params"
     (fun input ->
       Parser.map_tag
         "param"
         (fun input ->
-          match Parser.of_xml ?callback [] input with
+          match Parser.of_xml ?callback ?base64_decoder [] input with
           | Dict d ->
             if List.mem_assoc "Status" d
                && List.assoc "Status" d = String "Success"
@@ -440,7 +442,7 @@ let response_of_success ?callback input =
     input
 
 
-let response_of_input ?callback input =
+let response_of_input ?callback ?base64_decoder input =
   (match Xmlm.peek input with
   | `Dtd _ -> ignore (Xmlm.input input)
   | _ -> ());
@@ -449,8 +451,10 @@ let response_of_input ?callback input =
     (fun input ->
       Parser.skip_empty input;
       match Xmlm.peek input with
-      | `El_start ((_, "params"), _) -> response_of_success ?callback input
-      | `El_start ((_, "fault"), _) -> response_of_fault ?callback input
+      | `El_start ((_, "params"), _) ->
+          response_of_success ?callback ?base64_decoder input
+      | `El_start ((_, "fault"), _) ->
+          response_of_fault ?callback ?base64_decoder input
       | `El_start ((_, tag), _) ->
         parse_error (sprintf "open_tag(%s)" tag) "open_tag(fault/params)" input
       | `Data d -> parse_error (String.escaped d) "open_tag(fault/params)" input
@@ -459,11 +463,11 @@ let response_of_input ?callback input =
     input
 
 
-let response_of_string ?callback str =
+let response_of_string ?callback ?base64_decoder str =
   let input = Xmlm.make_input (`String (0, str)) in
-  response_of_input ?callback input
+  response_of_input ?callback ?base64_decoder input
 
 
-let response_of_in_channel ?callback chan =
+let response_of_in_channel ?callback ?base64_decoder chan =
   let input = Xmlm.make_input (`Channel chan) in
-  response_of_input ?callback input
+  response_of_input ?callback ?base64_decoder input
diff --git a/src/lib/xmlrpc.mli b/src/lib/xmlrpc.mli
index 09c91b5..ca78f22 100644
--- a/src/lib/xmlrpc.mli
+++ b/src/lib/xmlrpc.mli
@@ -22,40 +22,58 @@ val a_of_response
 
 exception Parse_error of string * string * Xmlm.input
 
+(** The parsing functions make it possible to specify the routine used to
+    decode base64 values. The default is to use [Base64.decode_exn] which
+    strictly interprets the standard. A different function will be required if
+    the XMLRPC server inserts line breaks into the base64 encoding (as per
+    RFC2045). *)
+
 val pretty_string_of_error : string -> string -> Xmlm.input -> string
 val parse_error : string -> string -> Xmlm.input -> unit
-val of_string : ?callback:(string list -> Rpc.t -> unit) -> string -> Rpc.t
+val of_string
+  : ?callback:(string list -> Rpc.t -> unit)
+  -> ?base64_decoder:(string -> string)
+  -> string -> Rpc.t
 
 val of_a
   :  ?callback:(string list -> Rpc.t -> unit)
+  -> ?base64_decoder:(string -> string)
   -> next_char:('b -> char option)
   -> 'b
   -> Rpc.t
   [@@ocaml.deprecated]
 
-val call_of_string : ?callback:(string list -> Rpc.t -> unit) -> string -> Rpc.call
+val call_of_string
+  : ?callback:(string list -> Rpc.t -> unit)
+  -> ?base64_decoder:(string -> string)
+  -> string -> Rpc.call
 
 val response_of_fault
   :  ?callback:(string list -> Rpc.t -> unit)
+  -> ?base64_decoder:(string -> string)
   -> Xmlm.input
   -> Rpc.response
 
 val response_of_success
   :  ?callback:(string list -> Rpc.t -> unit)
+  -> ?base64_decoder:(string -> string)
   -> Xmlm.input
   -> Rpc.response
 
 val response_of_input
   :  ?callback:(string list -> Rpc.t -> unit)
+  -> ?base64_decoder:(string -> string)
   -> Xmlm.input
   -> Rpc.response
 
 val response_of_string
   :  ?callback:(string list -> Rpc.t -> unit)
+  -> ?base64_decoder:(string -> string)
   -> string
   -> Rpc.response
 
 val response_of_in_channel
   :  ?callback:(string list -> Rpc.t -> unit)
+  -> ?base64_decoder:(string -> string)
   -> in_channel
   -> Rpc.response