diff --git a/src/core/CCByte_buffer.ml b/src/core/CCByte_buffer.ml
index 6cf63301..b2bdd448 100644
--- a/src/core/CCByte_buffer.ml
+++ b/src/core/CCByte_buffer.ml
@@ -136,6 +136,8 @@ let to_seq self =
     | Get_contents
     | Get of int
     | Clear
+    | Shrink_to of int
+    | Set of int * char
 
   let spf = Printf.sprintf
 
@@ -145,11 +147,15 @@ let to_seq self =
     | Get_contents -> "contents"
     | Get i -> spf "get %d" i
     | Clear -> "clear"
+    | Shrink_to n -> spf "shrink %d" n
+    | Set (i,c) -> spf "set %d %C" i c
 
   let gen_op size : (_*_) Gen.t =
     let open Gen in
     let base = if size>0 then
         [1, ((0--size) >|= fun x -> Get x, size);
+         1, ((0--size) >>= fun x -> printable >|= fun c -> Set (x,c), size);
+         1, ((0--size) >|= fun x -> Shrink_to x, x);
         ]
       else []
     in
@@ -177,8 +183,9 @@ let to_seq self =
       | Add_char _ :: tl -> loop (sz+1) tl
       | Clear :: tl -> loop 0 tl
       | Add_string s :: tl -> loop (sz+String.length s) tl
-      | Get n :: tl -> n < sz && loop sz tl
+      | (Get n | Set (n,_)) :: tl -> n < sz && loop sz tl
       | Get_contents :: tl -> loop sz tl
+      | Shrink_to x :: tl -> x <= sz && loop x tl
     in loop 0 ops
 
   let shrink_op = Iter.(function
@@ -186,6 +193,10 @@ let to_seq self =
     | Get n -> Shrink.int n >|= fun n->Get n
     | Add_char c -> Shrink.char c >|= fun c -> Add_char c
     | Add_string s -> Shrink.string s >|= fun s -> Add_string s
+    | Shrink_to n -> Shrink.int n >|= fun n -> Shrink_to n
+    | Set (n,c) ->
+      (Shrink.int n >|= fun n-> Set(n,c)) <+>
+      (Shrink.char c >|= fun c-> Set(n,c))
     )
 
   let arb = make gen ~print:(Print.list str_op)
@@ -193,33 +204,39 @@ let to_seq self =
 
   exception Nope of string
   let prop_consistent ops =
-    let buf = Buffer.create 32 in
+    let buf = ref "" in
     let b = create ~cap:32 () in
 
     let run_op op =
       match op with
       | Get i ->
-        assert (Buffer.length buf = length b);
-        let c1 = Buffer.nth buf i in
+        assert (String.length !buf = length b);
+        let c1 = (!buf).[i] in
         let c2 = get b i in
         if c1<>c2 then raise (Nope (spf "c1=%C, c2=%C" c1 c2))
 
       | Get_contents ->
-        let s1 = Buffer.contents buf in
+        let s1 = !buf in
         let s2 = contents b in
         if s1<>s2 then raise (Nope (spf "s1=%S, s2=%S" s1 s2))
 
-      | Add_char c -> Buffer.add_char buf c; add_char b c
-      | Add_string s -> Buffer.add_string buf s; append_string b s
-      | Clear -> Buffer.clear buf; clear b
-
+      | Add_char c -> buf := !buf ^ String.make 1 c; add_char b c
+      | Add_string s -> buf := !buf ^ s; append_string b s
+      | Clear -> buf := ""; clear b
+      | Shrink_to n -> buf := String.sub !buf 0 n; shrink_to b n
+      | Set (n,c) ->
+        (
+          let b' = Bytes.of_string !buf in
+          Bytes.set b' n c;
+          buf := Bytes.unsafe_to_string b';
+        );
+        set b n c
     in
 
     assume (is_valid ops);
     try List.iter run_op ops; true
     with Nope str ->
-      Test.fail_reportf "consistent ops failed:\n%s" str;
-      false
+      Test.fail_reportf "consistent ops failed:\n%s" str
 *)
 
 (*$Q