diff --git a/src/data/CCTrie.ml b/src/data/CCTrie.ml
index 422e7352..7527083b 100644
--- a/src/data/CCTrie.ml
+++ b/src/data/CCTrie.ml
@@ -559,6 +559,19 @@ module Make(W : WORD) = struct
       let t = S.of_list l in \
       S.check_invariants t)
   *)
+
+  (*$Q & ~small:List.length ~count:30
+    Q.(list_of_size Gen.(1 -- 20) (pair printable_string small_int)) \
+      (fun l -> let t = String.of_list l in \
+        List.for_all (fun (k,_) -> \
+          String.above k t |> Sequence.for_all (fun (k',v) -> k' >= k)) \
+          l)
+    Q.(list_of_size Gen.(1 -- 20) (pair printable_string small_int)) \
+      (fun l -> let t = String.of_list l in \
+        List.for_all (fun (k,_) -> \
+          String.below k t |> Sequence.for_all (fun (k',v) -> k' <= k)) \
+          l)
+  *)
 end
 
 module type ORDERED = sig
diff --git a/src/sexp/CCSexpM.ml b/src/sexp/CCSexpM.ml
index 52d0eb40..2dd9e49c 100644
--- a/src/sexp/CCSexpM.ml
+++ b/src/sexp/CCSexpM.ml
@@ -335,7 +335,7 @@ let parse_string s : t or_error =
 (*$inject
   let sexp_gen =
     let mkatom a = `Atom a and mklist l = `List l in
-    let atom = Q.Gen.(map mkatom (string_size (int_range 1 30))) in
+    let atom = Q.Gen.(map mkatom (string_size ~gen:printable (1 -- 30))) in
     let gen = Q.Gen.(
       sized (fix
         (fun self n st -> match n with
@@ -343,7 +343,7 @@ let parse_string s : t or_error =
         | _ ->
           frequency
             [ 1, atom
-            ; 2, map mklist (list_size (int_bound 10) (self (n/10)))
+            ; 2, map mklist (list_size (0 -- 10) (self (n/10)))
             ] st
         )
     )) in
@@ -365,7 +365,7 @@ let parse_string s : t or_error =
     | `List l -> List.for_all sexp_valid l
 *)
 
-(*$Q & ~count:30
+(*$Q & ~count:100
     sexp_gen (fun s -> sexp_valid s ==> (to_string s |> parse_string = `Ok s))
 *)