diff --git a/server/sexp.ml b/server/sexp.ml
index 37332fe..e913b32 100644
--- a/server/sexp.ml
+++ b/server/sexp.ml
@@ -30,11 +30,27 @@ and t =
 
 let compare a b = Pervasives.compare a b
 
+let digit_val c = (int_of_char c) - (int_of_char '0')
+let val_digit n = char_of_int (n + 48)
+
+let intstr =
+  let siz = 40 in
+  let buf = String.make siz (* enough for 128 bits *) ' ' in
+  function
+    | 0 -> "0"
+    | n ->
+      let rec loop n i =
+	if n = 0
+	then String.sub buf (siz - i) i
+	else (String.unsafe_set buf (siz - i - 1) (val_digit (n mod 10));
+	      loop (n / 10) (i + 1))
+      in loop n 0
+
 let generic_output_sexp write x =
   let rec walk x =
     match x with
       | Str s ->
-	lwt () = write (string_of_int (String.length s)) in
+	lwt () = write (intstr (String.length s)) in
 	lwt () = write ":" in
 	write s
       | Hint {hint = h; body = b} ->
@@ -85,8 +101,6 @@ let rec output_sexp_human ch x =
 let char_numeric c = '0' <= c && c <= '9'
 let char_whitespace c = c <= ' '
 
-let digit_val c = (int_of_char c) - (int_of_char '0')
-
 let input_bytes ch count =
   let buf = String.create count in (* mutable strings?!?! *)
   lwt () = read_into_exactly ch buf 0 count in