diff --git a/src/core/CCSexp.ml b/src/core/CCSexp.ml
index f31a2378..1c75df73 100644
--- a/src/core/CCSexp.ml
+++ b/src/core/CCSexp.ml
@@ -401,3 +401,24 @@ include (Make(struct
 *)
 
 let atom s : t = `Atom s
+
+(* regression for #338 *)
+(*$R
+  Printexc.record_backtrace true;
+  let cases = [
+    "\"\\256\"";
+    "\"\\722\02622222\\\\\n\r<\\\\\\\\\"\\222222222\\\\\"\"\2032!2222\\\\\"\"";
+    "\"\n\r<\\t\023\n\203\\622222222\\\\\"\"\2032!2222\\\\\"\"";
+    "\"\n\r<@t\023\n\203\\2222D2\n\r22222\01622222222222222222222222\203\\292242\222 2\\\\\">K2";
+    "\"\n\r<\\t\023\n\203\\272222222\\\\\"\"\2032\0042222\\\\\"\"";
+    "\"\023\n\203\\5222\n\r<\\t\023\n\203\\52222222\\\\\"2\\\216\216\216\216\216\\\\\"\216\216\216\216\216\216\216\216\216222222222222222\147";
+    "\"\\722\02622222\\\\\n\r<\\\\\\\\\"\\222222222\\\\\"\"\2032!2222\\\\\"\"";
+  ] in
+  cases
+  |> List.iter (fun s ->
+    try ignore (parse_string s);
+    with e ->
+      let st = Printexc.get_backtrace() in
+      print_endline @@ Printexc.to_string e ^ "\n" ^ st;
+      assert false)
+*)