diff --git a/forgejo/custom/public/assets/viewer.html b/forgejo/custom/public/assets/viewer.html
index 0f4b334..2040854 100644
--- a/forgejo/custom/public/assets/viewer.html
+++ b/forgejo/custom/public/assets/viewer.html
@@ -224,8 +224,8 @@
       <div class="field" style="flex:2">
         <label>query</label>
         <input id="query-input" class="ti" type="text"
-               placeholder="Name or Pset.Property"
-               title="Attribute or property set value to retrieve for each selected element"
+               placeholder="Name or Pset_X.Property"
+               title="Direct IFC attribute: Name, Description. Property set (dot notation required): Pset_WallCommon.FireRating, Qto_WallBaseQuantities.NetVolume"
                spellcheck="false">
       </div>
     </div>
diff --git a/ifcurl/service.py b/ifcurl/service.py
index e99a892..a16b786 100644
--- a/ifcurl/service.py
+++ b/ifcurl/service.py
@@ -787,6 +787,18 @@ def query(request: QueryRequest) -> JSONResponse:
     if not ifc_url.query:
         raise HTTPException(status_code=400, detail="URL has no 'query' parameter")
 
+    query_path = ifc_url.query
+    if "." not in query_path and (
+        query_path.startswith("Pset_") or query_path.startswith("Qto_")
+    ):
+        raise HTTPException(
+            status_code=400,
+            detail=(
+                f"'query={query_path}' looks like a property set name — "
+                f"use dot notation: '{query_path}.PropertyName'"
+            ),
+        )
+
     _ssrf_check(ifc_url)
 
     token = request.token