diff --git a/cmd/thanos/store.go b/cmd/thanos/store.go
index 1ec58f700a..5408d1443b 100644
--- a/cmd/thanos/store.go
+++ b/cmd/thanos/store.go
@@ -169,8 +169,8 @@ func (sc *storeConfig) registerFlag(cmd extkingpin.FlagClause) {
 	cmd.Flag("debug.estimated-max-series-size", "Estimated max series size. Setting a value might result in over fetching data while a small value might result in data refetch. Default value is 64KB.").
 		Hidden().Default(strconv.Itoa(store.EstimatedMaxSeriesSize)).Uint64Var(&sc.estimatedMaxSeriesSize)
 
-	cmd.Flag("estimated-series-size-stat", "Statistic to use to estimate block series size. This is currently used for lazy expanded posting series size estimation. Available options are max, p90, p99, p99, p9999 and zscore. If zscore is picked, the actual zscore value is set via estimated-series-size-zscore. Default value is "+string(store.BlockSeriesSizeMax)).
-		Default(string(store.BlockSeriesSizeMax)).
+	cmd.Flag("estimated-series-size-stat", "Statistic to use to estimate block series size. This is currently used for lazy expanded posting series size estimation. Available options are max, p90, p99, p99, p9999 and zscore. If zscore is picked, the actual zscore value is set via estimated-series-size-zscore.").
+		Default(string(store.BlockSeriesSizeZScore)).
 		EnumVar(&sc.estimatedSeriesSizeStat, string(store.BlockSeriesSizeMax), string(store.BlockSeriesSizeP90), string(store.BlockSeriesSizeP99), string(store.BlockSeriesSizeP999), string(store.BlockSeriesSizeP9999), string(store.BlockSeriesSizeZScore))
 
 	cmd.Flag("estimated-series-size-zscore", "Zscore is a statistical measurement that describes a value's relationship to the mean series size. Zscore 2 is calculated as average size + 2 * standard deviation. Use a larger zscore if you want a larger estimated series size. Default value is 2. Cannot be lower than 0.").
diff --git a/docs/components/store.md b/docs/components/store.md
index 6fe534ddce..8d7b7c018f 100644
--- a/docs/components/store.md
+++ b/docs/components/store.md
@@ -94,14 +94,13 @@ Flags:
                                  --no-cache-index-header option is specified.
       --enable-auto-gomemlimit   Enable go runtime to automatically limit memory
                                  consumption.
-      --estimated-series-size-stat=max
+      --estimated-series-size-stat=zscore
                                  Statistic to use to estimate block series size.
                                  This is currently used for lazy expanded
                                  posting series size estimation. Available
                                  options are max, p90, p99, p99, p9999 and
                                  zscore. If zscore is picked, the actual zscore
                                  value is set via estimated-series-size-zscore.
-                                 Default value is max
       --estimated-series-size-zscore=2
                                  Zscore is a statistical measurement that
                                  describes a value's relationship to the mean