diff --git a/.merlin b/.merlin
index 385d469..d904327 100644
--- a/.merlin
+++ b/.merlin
@@ -6,3 +6,4 @@ B _build/tests/
 B _build/bench/
 PKG oUnit
 PKG benchmark
+FLAG -safe-string
diff --git a/_oasis b/_oasis
index da48cfe..b84e725 100644
--- a/_oasis
+++ b/_oasis
@@ -30,6 +30,7 @@ Flag bigarray
 Library "sequence"
   Path:             .
   Modules:          Sequence
+  BuildDepends:     bytes
 
 Library "invert"
   Path:             invert
diff --git a/_tags b/_tags
index 5715982..45a0bee 100644
--- a/_tags
+++ b/_tags
@@ -28,3 +28,4 @@
 <bench/*.ml{,i}>: use_sequence
 # OASIS_STOP
 true: bin_annot
+true: safe_string
diff --git a/sequence.ml b/sequence.ml
index 00dd7cd..e6d3ca5 100644
--- a/sequence.ml
+++ b/sequence.ml
@@ -751,7 +751,7 @@ module IO = struct
     fun k ->
       let ic = open_in_gen flags mode filename in
       try
-        let buf = String.create size in
+        let buf = Bytes.create size in
         let n = ref 0 in
         let stop = ref false in
         while not !stop do
@@ -763,7 +763,7 @@ module IO = struct
             if n' = 0 then stop := true else n := !n + n';
           done;
           if !n > 0
-            then k (String.sub buf 0 !n)
+            then k (Bytes.sub_string buf 0 !n)
         done;
         close_in ic
       with e ->
@@ -773,12 +773,19 @@ module IO = struct
   let write_to ?(mode=0o644) ?(flags=[Open_creat;Open_wronly]) filename seq =
     let oc = open_out_gen flags mode filename in
     try
-      seq (fun s -> output oc s 0 (String.length s));
+      seq (fun s -> output oc s 0 (Bytes.length s));
       close_out oc
     with e ->
       close_out oc;
       raise e
 
+  let write_str_to ?mode ?flags filename seq =
+    write_to ?mode ?flags filename (map Bytes.unsafe_of_string seq)
+
   let write_lines ?mode ?flags filename seq =
-    write_to ?mode ?flags filename (snoc (intersperse "\n" seq) "\n")
+    let ret = Bytes.unsafe_of_string "\n" in
+    write_to ?mode ?flags filename (snoc (intersperse ret seq) ret)
+
+  let write_str_lines ?mode ?flags filename seq =
+    write_lines ?mode ?flags filename (map Bytes.unsafe_of_string seq)
 end
diff --git a/sequence.mli b/sequence.mli
index 5397de7..7664060 100644
--- a/sequence.mli
+++ b/sequence.mli
@@ -586,13 +586,19 @@ module IO : sig
       different iterations might return different results *)
 
   val write_to : ?mode:int -> ?flags:open_flag list ->
-                 string -> string t -> unit
+                 string -> Bytes.t t -> unit
   (** [write_to filename seq] writes all strings from [seq] into the given
       file. It takes care of opening and closing the file.
       @param mode default [0o644]
       @param flags used by [open_out_gen]. Default: [[Open_creat;Open_wronly]]. *)
 
+  val write_str_to : ?mode:int -> ?flags:open_flag list ->
+                     string -> string t -> unit
+
   val write_lines : ?mode:int -> ?flags:open_flag list ->
-                    string -> string t -> unit
+                    string -> Bytes.t t -> unit
   (** Same as {!write_to}, but intercales ['\n'] between each string *)
+
+  val write_str_lines : ?mode:int -> ?flags:open_flag list ->
+                        string -> string t -> unit
 end