diff --git a/src/proto_alpha/lib_protocol/src/alpha_context.mli b/src/proto_alpha/lib_protocol/src/alpha_context.mli
index 7d2aa8e00..a688f7847 100644
--- a/src/proto_alpha/lib_protocol/src/alpha_context.mli
+++ b/src/proto_alpha/lib_protocol/src/alpha_context.mli
@@ -265,6 +265,7 @@ module Constants : sig
 
   val preserved_cycles: context -> int
   val cycle_length: context -> int32
+  val blocks_per_commitment: context -> int32
   val voting_period_length: context -> int32
   val time_before_reward: context -> Period.t
   val slot_durations: context -> Period.t list
diff --git a/src/proto_alpha/lib_protocol/src/constants_repr.ml b/src/proto_alpha/lib_protocol/src/constants_repr.ml
index 590891ac9..b1e8af1df 100644
--- a/src/proto_alpha/lib_protocol/src/constants_repr.ml
+++ b/src/proto_alpha/lib_protocol/src/constants_repr.ml
@@ -47,6 +47,7 @@ let bootstrap_wealth =
 type constants = {
   preserved_cycles: int ;
   cycle_length: int32 ;
+  blocks_per_commitment: int32 ;
   voting_period_length: int32 ;
   time_before_reward: Period_repr.t ;
   slot_durations: Period_repr.t list ;
@@ -67,6 +68,7 @@ let read_public_key s = Ed25519.Public_key.of_hex_exn (`Hex s)
 let default = {
   preserved_cycles = 5 ;
   cycle_length = 2048l ;
+  blocks_per_commitment = 32l ;
   voting_period_length = 32768l ;
   time_before_reward =
     Period_repr.of_seconds_exn
@@ -120,6 +122,9 @@ let constants_encoding =
        and cycle_length =
          opt Compare.Int32.(=)
            default.cycle_length c.cycle_length
+       and blocks_per_commitment =
+         opt Compare.Int32.(=)
+           default.blocks_per_commitment c.blocks_per_commitment
        and voting_period_length =
          opt Compare.Int32.(=)
            default.voting_period_length c.voting_period_length
@@ -163,6 +168,7 @@ let constants_encoding =
        in
        ((( preserved_cycles,
            cycle_length,
+           blocks_per_commitment,
            voting_period_length,
            time_before_reward,
            slot_durations,
@@ -178,6 +184,7 @@ let constants_encoding =
            michelson_maximum_type_size)), ()) )
     (fun ((( preserved_cycles,
              cycle_length,
+             blocks_per_commitment,
              voting_period_length,
              time_before_reward,
              slot_durations,
@@ -195,6 +202,8 @@ let constants_encoding =
           unopt default.preserved_cycles preserved_cycles ;
         cycle_length =
           unopt default.cycle_length cycle_length ;
+        blocks_per_commitment =
+          unopt default.blocks_per_commitment blocks_per_commitment ;
         voting_period_length =
           unopt default.voting_period_length voting_period_length ;
         time_before_reward =
@@ -227,9 +236,10 @@ let constants_encoding =
     Data_encoding.(
       merge_objs
         (merge_objs
-           (obj9
+           (obj10
               (opt "preserved_cycles" uint8)
               (opt "cycle_length" int32)
+              (opt "blocks_per_commitment" int32)
               (opt "voting_period_length" int32)
               (opt "time_before_reward" int64)
               (opt "slot_durations" (list Period_repr.encoding))
diff --git a/src/proto_alpha/lib_protocol/src/constants_services.ml b/src/proto_alpha/lib_protocol/src/constants_services.ml
index 100092d10..81ae281b8 100644
--- a/src/proto_alpha/lib_protocol/src/constants_services.ml
+++ b/src/proto_alpha/lib_protocol/src/constants_services.ml
@@ -40,6 +40,14 @@ module S = struct
       ~output: (obj1 (req "voting_period_length" int32))
       RPC_path.(custom_root / "voting_period_length")
 
+  let blocks_per_commitment =
+    RPC_service.post_service
+      ~description: "How many blocks beetween random seed's nonce commitment"
+      ~query: RPC_query.empty
+      ~input: empty
+      ~output: (obj1 (req "blocks_per_commitment" int32))
+      RPC_path.(custom_root / "blocks_per_commitment")
+
   let time_before_reward =
     RPC_service.post_service
       ~description: "Time before reward"
@@ -110,6 +118,9 @@ let () =
   register0 S.voting_period_length begin fun ctxt () () ->
     return (Constants.voting_period_length ctxt)
   end ;
+  register0 S.blocks_per_commitment begin fun ctxt () () ->
+    return (Constants.blocks_per_commitment ctxt)
+  end ;
   register0 S.time_before_reward begin fun ctxt () () ->
     return (Constants.time_before_reward ctxt)
   end ;
@@ -138,6 +149,8 @@ let preserved_cycles ctxt block =
   RPC_context.make_call0 S.preserved_cycles ctxt block () ()
 let voting_period_length ctxt block =
   RPC_context.make_call0 S.voting_period_length ctxt block () ()
+let blocks_per_commitment ctxt block =
+  RPC_context.make_call0 S.blocks_per_commitment ctxt block () ()
 let time_before_reward ctxt block =
   RPC_context.make_call0 S.time_before_reward ctxt block () ()
 let slot_durations ctxt block =
diff --git a/src/proto_alpha/lib_protocol/src/constants_services.mli b/src/proto_alpha/lib_protocol/src/constants_services.mli
index 81060f60c..75664a92e 100644
--- a/src/proto_alpha/lib_protocol/src/constants_services.mli
+++ b/src/proto_alpha/lib_protocol/src/constants_services.mli
@@ -18,6 +18,9 @@ val cycle_length:
 val voting_period_length:
   'a #RPC_context.simple -> 'a -> int32 shell_tzresult Lwt.t
 
+val blocks_per_commitment:
+  'a #RPC_context.simple -> 'a -> int32 shell_tzresult Lwt.t
+
 val time_before_reward:
   'a #RPC_context.simple -> 'a -> Period.t shell_tzresult Lwt.t
 
diff --git a/src/proto_alpha/lib_protocol/src/constants_storage.ml b/src/proto_alpha/lib_protocol/src/constants_storage.ml
index a14a229f5..8a5a7df30 100644
--- a/src/proto_alpha/lib_protocol/src/constants_storage.ml
+++ b/src/proto_alpha/lib_protocol/src/constants_storage.ml
@@ -13,6 +13,9 @@ let preserved_cycles c =
 let cycle_length c =
   let constants = Raw_context.constants c in
   constants.cycle_length
+let blocks_per_commitment c =
+  let constants = Raw_context.constants c in
+  constants.blocks_per_commitment
 let voting_period_length c =
   let constants = Raw_context.constants c in
   constants.voting_period_length