diff --git a/src/resource.rs b/src/resource.rs
index a25881b..2bbfafc 100644
--- a/src/resource.rs
+++ b/src/resource.rs
@@ -21,6 +21,13 @@ pub async fn get_resource(
     question_id: String,
     alternative: String,
     feature_name: String,
+    // An empty map serializes as no `params` key at all on a real
+    // client-side call (unlike the server-only initial SSR call, which
+    // never round-trips through serialization) - without this, every
+    // `Resource::refetch()` after a fully-empty-params call failed with
+    // "missing field `params`", even though the very first load (always
+    // server-resolved) never did.
+    #[server(default)]
     params: std::collections::HashMap<String, String>,
 ) -> Result<serde_json::Value, ServerFnError> {
     use crate::server::AppState;
@@ -48,6 +55,8 @@ pub async fn get_requirement_options(
     alternative: String,
     feature_name: String,
     requirement_name: String,
+    // See get_resource's `params` for why this is needed.
+    #[server(default)]
     params: std::collections::HashMap<String, String>,
 ) -> Result<serde_json::Value, ServerFnError> {
     use crate::server::AppState;