diff --git a/ui/src/views/Forecast.jsx b/ui/src/views/Forecast.jsx
index 30815c1..6b726e1 100644
--- a/ui/src/views/Forecast.jsx
+++ b/ui/src/views/Forecast.jsx
@@ -1080,15 +1080,20 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
     const meta  = colMetaRef.current.find(c => c.cname === col)
     const group = meta?.dim_group && dimMembers[meta.dim_group]
 
-    // With the member list in hand this is a local lookup. It also answers where
-    // the source query could not: the source holds every attribute set a part ever
-    // had, so anything with more than one came back ambiguous and filled nothing.
-    // A member row is a single definition by construction.
-    let derived = null
-    if (group) {
-      derived = group.members.find(m => m.key_value === value.trim())?.attrs || null
-      if (!derived) return
-    } else {
+    // With the member list in hand this is a local lookup, and it answers where the
+    // source query could not: the source holds every attribute set a part ever had,
+    // so anything with more than one came back ambiguous and filled nothing. A
+    // member row is a single definition by construction.
+    //
+    // A miss is not an answer though. The list can be empty (never refreshed, or a
+    // refresh still running) or simply not contain this key, and in either case the
+    // source still knows. Falling back costs one request on a path that only runs
+    // when someone types a value.
+    let derived = group?.members?.length
+      ? (group.members.find(m => m.key_value === value.trim())?.attrs || null)
+      : null
+
+    if (!derived) {
       const res = await fetch(`/api/sources/${sourceId}/lookup?col=${encodeURIComponent(col)}&value=${encodeURIComponent(value)}`)
       if (!res.ok) return
       derived = await res.json()