diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5b9bc186f45..c50065e0309 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,8 @@ We use *breaking* word for marking changes that are not backward compatible (rel
 
 ## Unreleased
 
+- [#3010](https://github.com/thanos-io/thanos/pull/3010) Querier: Added a flag to override the the default look back delta in promql. The flag should be set to at least 2 times the slowest scrape interval.
+
 ## [v0.15.0](https://github.com/thanos-io/thanos/releases) - in release process.
 
 :warning: **WARNING** :warning: Thanos Rule's `/api/v1/rules` endpoint no longer returns the old, deprecated `partial_response_strategy`. The old, deprecated value has been fixed to `WARN` for quite some time. _Please_ use `partialResponseStrategy`.
@@ -52,7 +54,6 @@ sse_config:
 - [#2892](https://github.com/thanos-io/thanos/pull/2892) Receive: Receiver fails when the initial upload fails.
 - [#2865](https://github.com/thanos-io/thanos/pull/2865) ui: Migrate Thanos Ruler UI to React
 - [#2964](https://github.com/thanos-io/thanos/pull/2964) Query: Add time range parameters to label APIs. Add `start` and `end` fields to Store API `LabelNamesRequest` and `LabelValuesRequest`.
-- [#3010](https://github.com/thanos-io/thanos/pull/3010) Querier: Added a flag to set the default look back delta.
 - [#2996](https://github.com/thanos-io/thanos/pull/2996) Sidecar: Add `reloader_config_apply_errors_total` metric. Add new flags `--reloader.watch-interval`, and `--reloader.retry-interval`.
 - [#2973](https://github.com/thanos-io/thanos/pull/2973) Add Thanos Query Frontend component.
 - [#2980](https://github.com/thanos-io/thanos/pull/2980) Bucket Viewer: Migrate block viewer to React.
diff --git a/cmd/thanos/query.go b/cmd/thanos/query.go
index 409c856b186..183b825936b 100644
--- a/cmd/thanos/query.go
+++ b/cmd/thanos/query.go
@@ -70,7 +70,7 @@ func registerQuery(m map[string]setupFunc, app *kingpin.Application) {
 	maxConcurrentQueries := cmd.Flag("query.max-concurrent", "Maximum number of queries processed concurrently by query node.").
 		Default("20").Int()
 
-	lookbackDelta := cmd.Flag("query.lookback-delta", "The maximum lookback duration for retrieving metrics during expression evaluations.").Duration()
+	lookbackDelta := cmd.Flag("query.lookback-delta", "The maximum lookback duration for retrieving metrics during expression evaluations. Should be set to at least 2 times the slowest scrape interval to avoid gaps in the metrics.").Duration()
 
 	maxConcurrentSelects := cmd.Flag("query.max-concurrent-select", "Maximum number of select requests made concurrently per a query.").
 		Default("4").Int()