diff --git a/downstream.go b/downstream.go
index fee5134..0dc65ab 100644
--- a/downstream.go
+++ b/downstream.go
@@ -142,29 +142,30 @@ var needAllDownstreamCaps = map[string]string{
 //
 // This is only effective in single-upstream mode.
 var passthroughIsupport = map[string]bool{
-	"AWAYLEN":    true,
-	"BOT":        true,
-	"CHANLIMIT":  true,
-	"CHANMODES":  true,
-	"CHANNELLEN": true,
-	"CHANTYPES":  true,
-	"EXCEPTS":    true,
-	"EXTBAN":     true,
-	"HOSTLEN":    true,
-	"INVEX":      true,
-	"KICKLEN":    true,
-	"MAXLIST":    true,
-	"MAXTARGETS": true,
-	"MODES":      true,
-	"NAMELEN":    true,
-	"NETWORK":    true,
-	"NICKLEN":    true,
-	"PREFIX":     true,
-	"SAFELIST":   true,
-	"TARGMAX":    true,
-	"TOPICLEN":   true,
-	"USERLEN":    true,
-	"UTF8ONLY":   true,
+	"AWAYLEN":       true,
+	"BOT":           true,
+	"CHANLIMIT":     true,
+	"CHANMODES":     true,
+	"CHANNELLEN":    true,
+	"CHANTYPES":     true,
+	"CLIENTTAGDENY": true,
+	"EXCEPTS":       true,
+	"EXTBAN":        true,
+	"HOSTLEN":       true,
+	"INVEX":         true,
+	"KICKLEN":       true,
+	"MAXLIST":       true,
+	"MAXTARGETS":    true,
+	"MODES":         true,
+	"NAMELEN":       true,
+	"NETWORK":       true,
+	"NICKLEN":       true,
+	"PREFIX":        true,
+	"SAFELIST":      true,
+	"TARGMAX":       true,
+	"TOPICLEN":      true,
+	"USERLEN":       true,
+	"UTF8ONLY":      true,
 }
 
 type downstreamConn struct {