diff --git a/pkg/muxer/tcp/mux.go b/pkg/muxer/tcp/mux.go
index 5bf4fbc08..8302ab340 100644
--- a/pkg/muxer/tcp/mux.go
+++ b/pkg/muxer/tcp/mux.go
@@ -310,7 +310,7 @@ func alpn(tree *matchersTree, protos ...string) error {
 	return nil
 }
 
-var hostOrIP = regexp.MustCompile(`^[[:alnum:]\.\-\:]+$`)
+var hostOrIP = regexp.MustCompile(`^[[:word:]\.\-\:]+$`)
 
 // hostSNI checks if the SNI Host of the connection match the matcher host.
 func hostSNI(tree *matchersTree, hosts ...string) error {
diff --git a/pkg/muxer/tcp/mux_test.go b/pkg/muxer/tcp/mux_test.go
index 45820acdb..aa3c6b1e6 100644
--- a/pkg/muxer/tcp/mux_test.go
+++ b/pkg/muxer/tcp/mux_test.go
@@ -743,6 +743,11 @@ func Test_HostSNI(t *testing.T) {
 			ruleHosts:  []string{"foo.bar"},
 			serverName: "foo.bar",
 		},
+		{
+			desc:       "Matching hosts with subdomains with _",
+			ruleHosts:  []string{"foo_bar.example.com"},
+			serverName: "foo_bar.example.com",
+		},
 		{
 			desc:       "Matching IPv4",
 			ruleHosts:  []string{"127.0.0.1"},