diff --git a/internal/server/postgres/dataserverimpl_test.go b/internal/server/postgres/dataserverimpl_test.go
index d52b5ea..6a4a946 100644
--- a/internal/server/postgres/dataserverimpl_test.go
+++ b/internal/server/postgres/dataserverimpl_test.go
@@ -921,10 +921,10 @@ func TestGetForecastAsTimeseries(t *testing.T) {
 			}
 
 			resp, err := dc.GetForecastAsTimeseries(t.Context(), &pb.GetForecastAsTimeseriesRequest{
-				LocationUuid:      siteResp.LocationUuid,
-				HorizonMins:       uint32(tc.horizonMins),
-				Forecaster:        forecasterResp.Forecaster,
-				EnergySource:      pb.EnergySource_ENERGY_SOURCE_SOLAR,
+				LocationUuid: siteResp.LocationUuid,
+				HorizonMins:  uint32(tc.horizonMins),
+				Forecaster:   forecasterResp.Forecaster,
+				EnergySource: pb.EnergySource_ENERGY_SOURCE_SOLAR,
 				TimeWindow: &pb.TimeWindow{
 					StartTimestampUtc: timestamppb.New(pivotTime.Add(-time.Hour * 48)),
 					EndTimestampUtc:   timestamppb.New(pivotTime.Add(time.Hour * 36)),
diff --git a/internal/server/postgres/sql/queries/predictions.sql b/internal/server/postgres/sql/queries/predictions.sql
index 0a9347e..73219fb 100644
--- a/internal/server/postgres/sql/queries/predictions.sql
+++ b/internal/server/postgres/sql/queries/predictions.sql
@@ -400,16 +400,18 @@ relevant_predicted_values AS (
 deltas AS (
     SELECT
         rv.geometry_uuid,
-        rv.source_type_id,
-        rv.forecast_uuid,
-        rv.target_time_utc,
         rv.horizon_mins,
         rv.p50_sip - og.value_sip AS delta_sip
     FROM relevant_predicted_values AS rv
-        LEFT OUTER JOIN obs.observed_generation_values AS og USING (geometry_uuid, source_type_id)
+        INNER JOIN obs.observed_generation_values AS og
+        ON rv.geometry_uuid = og.geometry_uuid
+            AND rv.source_type_id = og.source_type_id
+            AND rv.target_time_utc = og.observation_timestamp_utc
     WHERE
         og.observer_uuid = $3
-        AND og.observation_timestamp_utc = rv.target_time_utc
+        AND og.geometry_uuid = ANY(sqlc.arg(geometry_uuids)::UUID [])
+        AND og.observation_timestamp_utc >= sqlc.arg(pivot_timestamp)::TIMESTAMP - INTERVAL '8 days'
+        AND og.observation_timestamp_utc < sqlc.arg(pivot_timestamp)::TIMESTAMP + INTERVAL '1 millisecond'
 )
 SELECT
     d.geometry_uuid,