diff --git a/internal/sub/masque_test.go b/internal/sub/masque_test.go
index 58572b629..85e46e3e1 100644
--- a/internal/sub/masque_test.go
+++ b/internal/sub/masque_test.go
@@ -114,3 +114,45 @@ func TestSubJsonServiceTurnsInboundHopIntoClientUDPHopMask(t *testing.T) {
 		t.Fatalf("client finalmask\n got: %s\nwant: %s", got, want)
 	}
 }
+
+// Every endpoint's config starts from the same parsed inbound finalmask; a host whose own
+// masks are merged in first must not use up the hop range the endpoints after it need.
+func TestSubJsonServiceKeepsUDPHopMaskOnEveryEndpoint(t *testing.T) {
+	inbound := &model.Inbound{
+		Listen: "203.0.113.10", Port: 443, Protocol: model.Hysteria, Remark: "hy",
+		Settings: `{"version":2,"clients":[{"email":"ivy@example.test","auth":"a"}]}`,
+		StreamSettings: `{"network":"hysteria","security":"tls",
+			"hysteriaSettings":{"version":2},
+			"tlsSettings":{"serverName":"hy.example.test","alpn":["h3"]},
+			"finalmask":{"quicParams":{"udpHop":{"ports":"20000-30000","interval":"5-10"}}},
+			"externalProxy":[
+				{"forceTls":"same","dest":"a.example.test","port":443,"remark":"a",
+					"finalMask":"{\"udp\":[{\"type\":\"salamander\",\"settings\":{\"password\":\"p\"}}]}"},
+				{"forceTls":"same","dest":"b.example.test","port":443,"remark":"b"}]}`,
+	}
+	client := model.Client{Email: "ivy@example.test", Auth: "a"}
+
+	configs := NewSubJsonService("", "", "", "", nil).getConfig(&SubService{address: "sub.example.com"}, inbound, client, "sub.example.com")
+	if len(configs) != 2 {
+		t.Fatalf("got %d configs, want one per endpoint", len(configs))
+	}
+	const hop = `{"settings":{"interval":"5-10","mode":"intervalRemote","remotePorts":"20000-30000"},"type":"udphop"}`
+	wants := []string{
+		`{"udp":[{"settings":{"password":"p"},"type":"salamander"},` + hop + `]}`,
+		`{"udp":[` + hop + `]}`,
+	}
+	for i, want := range wants {
+		var config struct {
+			Outbounds []struct {
+				StreamSettings map[string]any `json:"streamSettings"`
+			} `json:"outbounds"`
+		}
+		if err := json.Unmarshal(configs[i], &config); err != nil {
+			t.Fatalf("decode config %d: %v", i, err)
+		}
+		got, _ := json.Marshal(config.Outbounds[0].StreamSettings["finalmask"])
+		if string(got) != want {
+			t.Fatalf("endpoint %d finalmask\n got: %s\nwant: %s", i, got, want)
+		}
+	}
+}
diff --git a/internal/util/maskcompat/udphop.go b/internal/util/maskcompat/udphop.go
index f326f2621..85512a300 100644
--- a/internal/util/maskcompat/udphop.go
+++ b/internal/util/maskcompat/udphop.go
@@ -1,9 +1,13 @@
 package maskcompat
 
-import "strings"
+import (
+	"maps"
+	"slices"
+	"strings"
+)
 
-// UpgradeLegacyUDPHop moves the quicParams.udpHop range xray-core 26.9.9 stopped reading
-// into the client-only "udphop" UDP mask, whose intervalRemote mode is what the key did.
+// UpgradeLegacyUDPHop moves the quicParams.udpHop xray-core 26.9.9 ignores into an intervalRemote
+// "udphop" mask, rewriting only finalmask's own keys: a merged finalmask shares quicParams and udp.
 func UpgradeLegacyUDPHop(finalmask any) bool {
 	fm, _ := finalmask.(map[string]any)
 	quicParams, _ := fm["quicParams"].(map[string]any)
@@ -11,9 +15,12 @@ func UpgradeLegacyUDPHop(finalmask any) bool {
 	if !found {
 		return false
 	}
-	delete(quicParams, "udpHop")
-	if len(quicParams) == 0 {
+	restQuic := maps.Clone(quicParams)
+	delete(restQuic, "udpHop")
+	if len(restQuic) == 0 {
 		delete(fm, "quicParams")
+	} else {
+		fm["quicParams"] = restQuic
 	}
 
 	hop, _ := legacy.(map[string]any)
@@ -26,7 +33,7 @@ func UpgradeLegacyUDPHop(finalmask any) bool {
 		settings["interval"] = interval
 	}
 	masks, _ := fm["udp"].([]any)
-	fm["udp"] = append(masks, map[string]any{"type": "udphop", "settings": settings})
+	fm["udp"] = append(slices.Clip(masks), map[string]any{"type": "udphop", "settings": settings})
 	return true
 }