diff --git a/src/hash.ml b/src/hash.ml
index ca32519f..0a4d9002 100644
--- a/src/hash.ml
+++ b/src/hash.ml
@@ -49,7 +49,9 @@ module H64 = struct
 
   let of_octets s =
     match String.length s = 64 with
-    | false -> Fmt.failwith "Hash.of_octets failure: data is not 64 bytes"
+    | false ->
+        Fmt.epr "s length: %d@." (String.length s);
+        Fmt.failwith "Hash.of_octets failure: data is not 64 bytes"
     | true -> SHA512.of_raw_string s
 
   let to_octets v =
diff --git a/test/b32.ml b/test/b32.ml
index c6986084..1858461f 100644
--- a/test/b32.ml
+++ b/test/b32.ml
@@ -1,6 +1,6 @@
 let () =
   let id s = s |> B32.encode |> B32.decode |> Result.get_ok in
-  let f s =
+  let round_trip s =
     let s' = id s in
     match s' = s with
     | false ->
@@ -8,8 +8,25 @@ let () =
     | true -> ()
   in
   let s = String.init 0xff Char.chr in
+  round_trip s;
   let s_l = List.init 0x0f (fun i -> String.init i Char.chr) in
-  f s;
-  List.iter f s_l;
+  List.iter round_trip s_l; ()
+
+let () =
+  let input = "91JPRV3F5GG4EKJNDSJQ8" in
+  Fmt.epr "input length: %d@." (String.length input);
+  let output =
+    input
+    |> Hash.H64.of_b32
+    |> Result.get_ok
+    |> Hash.H64.to_octets
+    |> B32.encode
+  in
+  let expected =
+    "D0R24RZ1TPASVQ2NY56CT8AJDYZE9ZGDB0GVZ05E9D4YGZQW2RC5YFPQ0Q86EPW836DY7VYQTNFFJT3ZR2K508F4JVS5JNJKYN2MMFR"
+  in
+  Fmt.pr "input   : %s@." input;
+  Fmt.pr "output  : %s@." output;
+  Fmt.pr "expected: %s@." expected;
 
   ()
diff --git a/test/dune b/test/dune
index bec41ef4..3c54d887 100644
--- a/test/dune
+++ b/test/dune
@@ -6,7 +6,7 @@
 (test
  (name b32)
  (modules b32)
- (libraries b32 fmt))
+ (libraries mte b32 fmt))
 
 ; TODO
 ; cram test?