diff --git a/cmd/thanos/query.go b/cmd/thanos/query.go
index 09f86aaf4e2..75a29ee9fce 100644
--- a/cmd/thanos/query.go
+++ b/cmd/thanos/query.go
@@ -11,6 +11,7 @@ import (
 	"strings"
 	"time"
 
+	extflag "github.com/efficientgo/tools/extkingpin"
 	"google.golang.org/grpc"
 
 	"github.com/go-kit/log"
@@ -209,7 +210,13 @@ func registerQuery(app *extkingpin.App) {
 		Default("1s"))
 
 	storeResponseTimeout := extkingpin.ModelDuration(cmd.Flag("store.response-timeout", "If a Store doesn't send any data in this specified duration then a Store will be ignored and partial data will be returned if it's enabled. 0 disables timeout.").Default("0ms"))
-	storeSelectorRelabelConf := *extkingpin.RegisterSelectorRelabelFlags(cmd)
+
+	storeSelectorRelabelConf := *extflag.RegisterPathOrContent(
+		cmd,
+		"selector.relabel-config",
+		"YAML with relabeling configuration that allows the Querier to select specific TSDBs by their external label. It follows native Prometheus relabel-config syntax. See format details: https://prometheus.io/docs/prometheus/latest/configuration/configuration/#relabel_config ",
+		extflag.WithEnvSubstitution(),
+	)
 
 	reqLogConfig := extkingpin.RegisterRequestLoggingFlags(cmd)
 
diff --git a/docs/components/query.md b/docs/components/query.md
index 83a30b04400..59aa9ed783a 100644
--- a/docs/components/query.md
+++ b/docs/components/query.md
@@ -462,16 +462,17 @@ Flags:
                                  info endpoint (repeated).
       --selector.relabel-config=<content>
                                  Alternative to 'selector.relabel-config-file'
-                                 flag (mutually exclusive). Content of
-                                 YAML file that contains relabeling
-                                 configuration that allows selecting
-                                 blocks. It follows native Prometheus
+                                 flag (mutually exclusive). Content of YAML
+                                 with relabeling configuration that allows
+                                 the Querier to select specific TSDBs by their
+                                 external label. It follows native Prometheus
                                  relabel-config syntax. See format details:
                                  https://prometheus.io/docs/prometheus/latest/configuration/configuration/#relabel_config
       --selector.relabel-config-file=<file-path>
-                                 Path to YAML file that contains relabeling
-                                 configuration that allows selecting
-                                 blocks. It follows native Prometheus
+                                 Path to YAML with relabeling configuration
+                                 that allows the Querier to select
+                                 specific TSDBs by their external label.
+                                 It follows native Prometheus
                                  relabel-config syntax. See format details:
                                  https://prometheus.io/docs/prometheus/latest/configuration/configuration/#relabel_config
       --store=<store> ...        Deprecation Warning - This flag is deprecated