diff --git a/src/proto_alpha/lib_protocol/sc_rollup_arith.ml b/src/proto_alpha/lib_protocol/sc_rollup_arith.ml
index 7f9761f3525c6c1bb8e17a53d6df09c611abfa55..94a9b9e343d611999994db759ad587a1fafccc94 100644
--- a/src/proto_alpha/lib_protocol/sc_rollup_arith.ml
+++ b/src/proto_alpha/lib_protocol/sc_rollup_arith.ml
@@ -681,7 +681,7 @@ module Make (Context : P) :
 
       let name = "output_counter"
 
-      let encoding = Data_encoding.z
+      let encoding = Data_encoding.n
 
       let pp = Z.pp_print
     end)
diff --git a/src/proto_alpha/lib_protocol/sc_rollup_inbox_repr.ml b/src/proto_alpha/lib_protocol/sc_rollup_inbox_repr.ml
index 6c89524a2d2fe0078869aec20c66023b4fcab6e1..036624056bb21c048bfde0680dbac10cf79e90b2 100644
--- a/src/proto_alpha/lib_protocol/sc_rollup_inbox_repr.ml
+++ b/src/proto_alpha/lib_protocol/sc_rollup_inbox_repr.ml
@@ -383,7 +383,7 @@ let of_versioned = function V1 inbox -> inbox [@@inline]
 let to_versioned inbox = V1 inbox [@@inline]
 
 let key_of_message ix =
-  ["message"; Data_encoding.Binary.to_string_exn Data_encoding.z ix]
+  ["message"; Data_encoding.Binary.to_string_exn Data_encoding.n ix]
 
 let level_key = ["level"]