diff --git a/src/parse_config.ml b/src/parse_config.ml
index 5e191bd8..044873fb 100644
--- a/src/parse_config.ml
+++ b/src/parse_config.ml
@@ -178,7 +178,22 @@ let yes_no = function
   | s -> fail "expected `YES`/`NO` value, got `%s`" s
 
 let uri s = Uri.of_string s
-let amount s = s |> Amount.of_string |> unwrap
+
+let amount =
+  let currency = ref None in
+  fun s ->
+    let amount = s |> Amount.of_string |> unwrap in
+    match !currency with
+    | None ->
+        currency := Some amount.currency;
+        amount
+    | Some cur -> (
+        match String.equal amount.currency cur with
+        | false ->
+            fail "only one kind of currency is supported, found: `%s` and `%s`."
+              amount.currency cur
+        | true -> amount)
+
 let duration s = Config_duration.(s |> parse |> to_time_span)
 
 let ed25519 s =