diff --git a/frontend/src/components/FinalMaskForm.tsx b/frontend/src/components/FinalMaskForm.tsx
index e43b689e..91671515 100644
--- a/frontend/src/components/FinalMaskForm.tsx
+++ b/frontend/src/components/FinalMaskForm.tsx
@@ -91,7 +91,7 @@ function defaultQuicParams(): Record<string, unknown> {
     brutalUp: 0,
     brutalDown: 0,
     hasUdpHop: false,
-    udpHop: { ports: '20000-50000', interval: 5 },
+    udpHop: { ports: '20000-50000', interval: '5-10' },
     maxIdleTimeout: 30,
     keepAlivePeriod: 10,
     disablePathMTUDiscovery: false,
@@ -707,7 +707,7 @@ function QuicParamsForm({ base, form }: { base: (string | number)[]; form: FormI
             <Input placeholder="e.g. 20000-50000" />
           </Form.Item>
           <Form.Item label="Hop Interval (s)" name={[...base, 'udpHop', 'interval']}>
-            <InputNumber min={5} />
+            <Input placeholder="e.g. 5-10" />
           </Form.Item>
         </>
       )}
diff --git a/frontend/src/schemas/protocols/stream/finalmask.ts b/frontend/src/schemas/protocols/stream/finalmask.ts
index 79326978..83d06808 100644
--- a/frontend/src/schemas/protocols/stream/finalmask.ts
+++ b/frontend/src/schemas/protocols/stream/finalmask.ts
@@ -47,10 +47,16 @@ export type QuicCongestion = z.infer<typeof QuicCongestionSchema>;
 
 // udpHop randomizes the QUIC port between a range every `interval` seconds
 // to dodge port-based blocking. Both fields are dash-range strings on the
-// wire (e.g. '20000-50000', '5-10').
+// wire (e.g. '20000-50000', '5-10'). preprocess coerces legacy DB rows
+// where interval was stored as a number (UI bug — see B19 in commit history).
+const StringRangeSchema = z.preprocess(
+  (v) => (typeof v === 'number' ? String(v) : v),
+  z.string(),
+);
+
 export const QuicUdpHopSchema = z.object({
-  ports: z.string().default('20000-50000'),
-  interval: z.string().default('5-10'),
+  ports: StringRangeSchema.default('20000-50000'),
+  interval: StringRangeSchema.default('5-10'),
 });
 export type QuicUdpHop = z.infer<typeof QuicUdpHopSchema>;