diff --git a/examples/specs/bar_month_temporal.vl.json b/examples/specs/bar_month_temporal.vl.json
index 622814fa34..7b0aae110f 100644
--- a/examples/specs/bar_month_temporal.vl.json
+++ b/examples/specs/bar_month_temporal.vl.json
@@ -3,7 +3,7 @@
   "data": {"url": "data/seattle-weather.csv"},
   "mark": "bar",
   "encoding": {
-    "x": {"timeUnit": "month", "field": "date"},
+    "x": {"timeUnit": "month", "field": "date", "type": "temporal"},
     "y": {"aggregate": "mean", "field": "precipitation"}
   }
 }