diff --git a/examples/specs/area_cumulative_freq.vl.json b/examples/specs/area_cumulative_freq.vl.json
index 82a51396bb..f0a5469471 100644
--- a/examples/specs/area_cumulative_freq.vl.json
+++ b/examples/specs/area_cumulative_freq.vl.json
@@ -2,8 +2,12 @@
   "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
   "data": {"url": "data/movies.json"},
   "transform": [{
+    "aggregate":[{"op": "count", "field": "*", "as": "count"}],
+    "groupby": ["IMDB Rating"]
+  },
+  {
     "sort": [{"field": "IMDB Rating"}],
-    "window": [{"op": "count", "field": "count", "as": "Cumulative Count"}],
+    "window": [{"op": "sum", "field": "count", "as": "Cumulative Count"}],
     "frame": [null, 0]
   }],
   "mark": "area",
@@ -14,8 +18,7 @@
     },
     "y": {
       "field": "Cumulative Count",
-      "type": "quantitative",
-      "aggregate": "max"
+      "type": "quantitative"
     }
   }
 }
diff --git a/src/normalize/pathoverlay.ts b/src/normalize/pathoverlay.ts
index c2e7d310ad..92172f5684 100644
--- a/src/normalize/pathoverlay.ts
+++ b/src/normalize/pathoverlay.ts
@@ -132,6 +132,7 @@ export class PathOverlayNormalizer implements NonFacetUnitNormalizer<UnitSpecWit
     // FIXME: determine rules for applying selections.
 
     // Need to copy stack config to overlayed layer
+    // FIXME: normalizer shouldn't call `initMarkdef`, a method from an init phase.
     const stackProps = stack(initMarkdef(markDef, encoding, config), encoding);
 
     let overlayEncoding = encoding;