diff --git a/src/telegram/bot/helpers.test.ts b/src/telegram/bot/helpers.test.ts
index ebc774b92..526d2ec3a 100644
--- a/src/telegram/bot/helpers.test.ts
+++ b/src/telegram/bot/helpers.test.ts
@@ -169,6 +169,22 @@ describe("normalizeForwardedContext", () => {
     expect(ctx?.from).toBe("My Channel (New Sig)");
   });
 
+  it("returns undefined signature when author_signature is blank", () => {
+    const ctx = normalizeForwardedContext({
+      forward_origin: {
+        type: "channel",
+        chat: { title: "Updates", id: -100333, type: "channel" },
+        date: 860,
+        author_signature: "   ",
+        message_id: 1,
+      },
+      // oxlint-disable-next-line typescript/no-explicit-any
+    } as any);
+    expect(ctx).not.toBeNull();
+    expect(ctx?.fromSignature).toBeUndefined();
+    expect(ctx?.from).toBe("Updates");
+  });
+
   it("handles forward_origin channel without author_signature", () => {
     const ctx = normalizeForwardedContext({
       forward_origin: {
diff --git a/src/telegram/bot/helpers.ts b/src/telegram/bot/helpers.ts
index af2682ada..4b46db1cc 100644
--- a/src/telegram/bot/helpers.ts
+++ b/src/telegram/bot/helpers.ts
@@ -253,6 +253,8 @@ export function describeReplyTarget(msg: Message): TelegramReplyTarget | null {
   };
 }
 
+export type TelegramChatType = "private" | "group" | "supergroup" | "channel";
+
 export type TelegramForwardedContext = {
   from: string;
   date?: number;
@@ -262,7 +264,7 @@ export type TelegramForwardedContext = {
   fromTitle?: string;
   fromSignature?: string;
   /** Original chat type from forward_from_chat (e.g. "channel", "supergroup", "group"). */
-  fromChatType?: string;
+  fromChatType?: TelegramChatType;
   /** Original message ID in the source chat (channel forwards). */
   fromMessageId?: number;
 };
@@ -336,7 +338,7 @@ function buildForwardedContextFromChat(params: {
   }
   const signature = params.signature?.trim() || undefined;
   const from = signature ? `${display} (${signature})` : display;
-  const chatType = params.chat.type?.trim() || undefined;
+  const chatType = (params.chat.type?.trim() || undefined) as TelegramChatType | undefined;
   return {
     from,
     date: params.date,