diff --git a/src/proto_alpha/lib_protocol/adaptive_inflation_storage.ml b/src/proto_alpha/lib_protocol/adaptive_inflation_storage.ml
index e29d402c7358e991f871ed3fedd9097863ed8844..b9b30eec684c94c6f2c16011dd186512781e88dd 100644
--- a/src/proto_alpha/lib_protocol/adaptive_inflation_storage.ml
+++ b/src/proto_alpha/lib_protocol/adaptive_inflation_storage.ml
@@ -42,8 +42,46 @@ let ratio_to_bonus q = Q.(q * of_int64 bonus_unit |> to_int64)
 
 let max_bonus = Int64.div bonus_unit 20L (* = 5% *)
 
+type error += Undetermined_inflation_coeff_for_cycle of Cycle_repr.t
+
+let () =
+  let open Data_encoding in
+  let undetermined_inflation_coeff_for_cycle_description =
+    "Inflation coefficient is only determined for the current cycle and the \
+     next [preserved_cycles] cycles to come. Requested cycle is not in this \
+     window."
+  in
+  register_error_kind
+    `Permanent
+    ~id:"undetermined_inflation_coeff_for_cycle"
+    ~title:"Undetermined inflation coeff for cycle"
+    ~description:undetermined_inflation_coeff_for_cycle_description
+    ~pp:(fun ppf cycle ->
+      Format.fprintf
+        ppf
+        "%s (cycle %a)"
+        undetermined_inflation_coeff_for_cycle_description
+        Cycle_repr.pp
+        cycle)
+    (obj1 (req "Undetermined_inflation_coeff_for_cycle" Cycle_repr.encoding))
+    (function
+      | Undetermined_inflation_coeff_for_cycle cycle -> Some cycle | _ -> None)
+    (fun cycle -> Undetermined_inflation_coeff_for_cycle cycle)
+
+let check_determined_cycle ctxt cycle =
+  let ai_enable = Constants_storage.adaptive_inflation_enable ctxt in
+  if ai_enable then
+    let ctxt_cycle = (Raw_context.current_level ctxt).cycle in
+    let preserved_cycles = Constants_storage.preserved_cycles ctxt in
+    fail_unless
+      Cycle_repr.(
+        ctxt_cycle <= cycle && cycle <= add ctxt_cycle preserved_cycles)
+      (Undetermined_inflation_coeff_for_cycle cycle)
+  else return_unit
+
 let get_reward_coeff ctxt ~cycle =
   let open Lwt_result_syntax in
+  let* () = check_determined_cycle ctxt cycle in
   let ai_enable = Constants_storage.adaptive_inflation_enable ctxt in
   if ai_enable then
     (* Even if AI is enabled, the storage can be empty: this is the case for
diff --git a/src/proto_alpha/lib_protocol/adaptive_inflation_storage.mli b/src/proto_alpha/lib_protocol/adaptive_inflation_storage.mli
index 6702480230a53e03097d89fda6c7ce0d115b94c8..82116b087501508ad19c62039c1888ae0f8db109 100644
--- a/src/proto_alpha/lib_protocol/adaptive_inflation_storage.mli
+++ b/src/proto_alpha/lib_protocol/adaptive_inflation_storage.mli
@@ -68,10 +68,11 @@ val launch_cycle : Raw_context.t -> Cycle_repr.t option tzresult Lwt.t
 module For_RPC : sig
   (** [get_reward_coeff ctxt cycle] reads the reward coeff for the given cycle
       from the storage.
-      Returns [Q.one] if the given cycle is not between [current_cycle] and
+
+      Fails if the given cycle is not between [current_cycle] and
       [current_cycle + preserved_cycles].
-      If adaptive inflation has not been activated, or has been activated and the
-      given cycle is less than [preserved_cycles] after the activation cycle,
+
+      If adaptive inflation has not been activated,
       then this function returns [Q.one].
       Used only for RPCs. To get the actual rewards, use [Delegate_rewards]. *)
   val get_reward_coeff :