diff --git a/src/channels/plugins/onboarding/signal.ts b/src/channels/plugins/onboarding/signal.ts
index d75577ad1..e702e29e8 100644
--- a/src/channels/plugins/onboarding/signal.ts
+++ b/src/channels/plugins/onboarding/signal.ts
@@ -235,12 +235,20 @@ export const signalOnboardingAdapter: ChannelOnboardingAdapter = {
     }
 
     if (!account) {
-      account = String(
+      const rawAccount = String(
         await prompter.text({
           message: "Signal bot number (E.164)",
-          validate: (value) => (value?.trim() ? undefined : "Required"),
+          validate: (value) => {
+            const trimmed = value?.trim();
+            if (!trimmed) return "Required";
+            if (!normalizeE164(trimmed)) {
+              return "Invalid E.164 phone number (must start with + and country code, e.g. +15555550123)";
+            }
+            return undefined;
+          },
         }),
       ).trim();
+      account = normalizeE164(rawAccount) ?? rawAccount;
     }
 
     if (account) {