diff --git a/mirage-crypto-rng.opam b/mirage-crypto-rng.opam
index 47204de0..701c88cc 100644
--- a/mirage-crypto-rng.opam
+++ b/mirage-crypto-rng.opam
@@ -22,7 +22,7 @@ depends: [
   "digestif" {>= "1.1.4"}
   "ounit2" {with-test}
   "randomconv" {with-test & >= "0.2.0"}
-  "ohex" {with-test}
+  "ohex" {with-test & >= "0.2.0"}
 ]
 conflicts: [ "mirage-runtime" {< "3.8.0"} ]
 description: """
diff --git a/mirage-crypto.opam b/mirage-crypto.opam
index 6bcbc78b..484cda49 100644
--- a/mirage-crypto.opam
+++ b/mirage-crypto.opam
@@ -17,7 +17,7 @@ depends: [
   "dune" {>= "2.7"}
   "dune-configurator" {>= "2.0.0"}
   "ounit2" {with-test}
-  "ohex" {with-test}
+  "ohex" {with-test & >= "0.2.0"}
   "eqaf" {>= "0.8"}
 ]
 conflicts: [
diff --git a/tests/test_common.ml b/tests/test_common.ml
index 2767aaca..10c19c51 100644
--- a/tests/test_common.ml
+++ b/tests/test_common.ml
@@ -48,7 +48,7 @@ let eq_opt eq a b = match (a, b) with
   | (Some x, Some y) -> eq x y
   | _                -> false
 
-let pp_octets pp = pp (Ohex.pp ())
+let pp_octets pp = pp (Ohex.pp_hexdump ())
 
 let assert_oct_equal ?msg =
   assert_equal ~cmp:String.equal ?msg ~pp_diff:(pp_octets pp_diff)
diff --git a/tests/test_dh.ml b/tests/test_dh.ml
index d4bfee42..20465d16 100644
--- a/tests/test_dh.ml
+++ b/tests/test_dh.ml
@@ -15,7 +15,7 @@ let dh_selftest ~bits n =
       ~cmp:(eq_opt String.equal)
       ~pp_diff:(pp_diff (fun ppf -> function
           | None -> Format.fprintf ppf "None"
-          | Some a -> Format.fprintf ppf "Some(%a)" (Ohex.pp ()) a))
+          | Some a -> Format.fprintf ppf "Some(%a)" (Ohex.pp_hexdump ()) a))
       ~msg:"shared secret"
 
 let dh_shared_0 =
diff --git a/tests/test_eio_entropy_collection.ml b/tests/test_eio_entropy_collection.ml
index 71969725..b2764517 100644
--- a/tests/test_eio_entropy_collection.ml
+++ b/tests/test_eio_entropy_collection.ml
@@ -8,12 +8,12 @@ module Printing_rng = struct
   let pools = 1
 
   let reseed ~g:_ data =
-    Format.printf "reseeding: %a@.%!"  (Ohex.pp ()) data
+    Format.printf "reseeding:@.%a@.%!" (Ohex.pp_hexdump ()) data
 
   let accumulate ~g:_ source =
     let print data =
       Format.printf "accumulate: (src: %a) %a@.%!"
-        Mirage_crypto_rng.Entropy.pp_source source  (Ohex.pp ()) data
+        Mirage_crypto_rng.Entropy.pp_source source Ohex.pp data
     in
     `Acc print
 end
diff --git a/tests/test_entropy.ml b/tests/test_entropy.ml
index 59d46c3e..f0984d38 100644
--- a/tests/test_entropy.ml
+++ b/tests/test_entropy.ml
@@ -13,7 +13,7 @@ let cpu_bootstrap_check () =
         try
           let data' = cpu_rng_bootstrap 1 in
           if String.equal !data data' then begin
-            Ohex.pp () Format.std_formatter data';
+            Ohex.pp Format.std_formatter data';
             failwith ("same data from CPU bootstrap at " ^ string_of_int i);
           end;
           data := data'
@@ -24,7 +24,7 @@ let whirlwind_bootstrap_check () =
   for i = 0 to 10 do
     let data' = Mirage_crypto_rng.Entropy.whirlwind_bootstrap 1 in
     if String.equal !data data' then begin
-      Ohex.pp () Format.std_formatter data';
+      Ohex.pp Format.std_formatter data';
       failwith ("same data from whirlwind bootstrap at " ^ string_of_int i);
     end;
     data := data'
@@ -34,7 +34,7 @@ let timer_check () =
   for i = 0 to 10 do
     let data' = Mirage_crypto_rng.Entropy.interrupt_hook () () in
     if String.equal !data data' then begin
-      Ohex.pp () Format.std_formatter data';
+      Ohex.pp Format.std_formatter data';
       failwith ("same data from timer at " ^ string_of_int i);
     end;
     data := data'
diff --git a/tests/test_entropy_collection.ml b/tests/test_entropy_collection.ml
index ac588e0b..bed653b2 100644
--- a/tests/test_entropy_collection.ml
+++ b/tests/test_entropy_collection.ml
@@ -10,12 +10,12 @@ module Printing_rng = struct
   let generate_into ~g:_ _buf ~off:_ _len = assert false
 
   let reseed ~g:_ data =
-    Format.printf "reseeding: %a@.%!" (Ohex.pp ()) data
+    Format.printf "reseeding:@.%a@.%!" (Ohex.pp_hexdump ()) data
 
   let accumulate ~g:_ source =
     let print data =
       Format.printf "accumulate: (src: %a) %a@.%!"
-        Mirage_crypto_rng.Entropy.pp_source source (Ohex.pp ()) data
+        Mirage_crypto_rng.Entropy.pp_source source Ohex.pp data
     in
     `Acc print
 
diff --git a/tests/test_entropy_collection_async.ml b/tests/test_entropy_collection_async.ml
index 29e434b8..d2331249 100644
--- a/tests/test_entropy_collection_async.ml
+++ b/tests/test_entropy_collection_async.ml
@@ -11,12 +11,12 @@ module Printing_rng = struct
   let generate_into ~g:_ _buf ~off:_ _len = assert false
 
   let reseed ~g:_ data =
-    Format.printf "reseeding: %a@.%!" (Ohex.pp ()) data
+    Format.printf "reseeding:@.%a@.%!" (Ohex.pp_hexdump ()) data
 
   let accumulate ~g:_ source =
     let print data =
       Format.printf "accumulate: (src: %a) %a@.%!"
-        Mirage_crypto_rng.Entropy.pp_source source  (Ohex.pp ()) data
+        Mirage_crypto_rng.Entropy.pp_source source Ohex.pp data
     in
     `Acc print