diff --git a/src/github/webhook.ts b/src/github/webhook.ts
index e2c9c0f992..0691c77428 100644
--- a/src/github/webhook.ts
+++ b/src/github/webhook.ts
@@ -37,7 +37,11 @@ export async function handleGitHubWebhook(c: Context<{ Bindings: Env }>): Promis
 
   const payloadHash = await sha256Hex(rawBody);
   const existingEvent = await getWebhookEvent(c.env, deliveryId);
-  if (existingEvent && existingEvent.payloadHash === payloadHash && existingEvent.status !== "error") {
+  // Suppress redelivery of an already-processed event (on success its payloadHash is overwritten to a
+  // "processed" sentinel, so a hash match alone misses it and the event re-runs its side effects) or one
+  // still in flight with the same payload. "error" rows are never suppressed so a failed enqueue/processing
+  // can still be retried (#789).
+  if (existingEvent && existingEvent.status !== "error" && (existingEvent.status === "processed" || existingEvent.payloadHash === payloadHash)) {
     return c.json({ ok: true, deliveryId, eventName, status: "duplicate" }, 202);
   }
 
diff --git a/test/unit/webhook.test.ts b/test/unit/webhook.test.ts
index 70774b6323..9ebf7ddb8c 100644
--- a/test/unit/webhook.test.ts
+++ b/test/unit/webhook.test.ts
@@ -1,7 +1,7 @@
 import { describe, expect, it } from "vitest";
 import type { Context } from "hono";
 import { handleGitHubWebhook } from "../../src/github/webhook";
-import { getWebhookEvent } from "../../src/db/repositories";
+import { getWebhookEvent, recordWebhookEvent } from "../../src/db/repositories";
 import { createTestEnv } from "../helpers/d1";
 
 describe("github webhook body reader edge cases", () => {
@@ -76,6 +76,46 @@ describe("github webhook enqueue failure (#786)", () => {
   });
 });
 
+describe("github webhook dedup (#789)", () => {
+  it("suppresses redelivery of an already-processed event instead of re-running side effects", async () => {
+    const env = createTestEnv();
+    let sendCount = 0;
+    env.JOBS = {
+      send: async () => {
+        sendCount += 1;
+      },
+    } as unknown as typeof env.JOBS;
+    // Seed a fully-processed event: on success the queue overwrites payloadHash with the "processed"
+    // sentinel, so a redelivery carries the real hash and a hash-only dedup would miss it.
+    await recordWebhookEvent(env, { deliveryId: "redelivery-1", eventName: "pull_request", payloadHash: "processed", status: "processed" });
+    const rawBody = JSON.stringify({ action: "opened", repository: { full_name: "JSONbored/gittensory" } });
+    const signature = await signWebhook(rawBody, env.GITHUB_WEBHOOK_SECRET);
+    const request = new Request("https://example.com/webhook", { method: "POST", body: rawBody });
+    const headers: Record<string, string> = {
+      "x-github-delivery": "redelivery-1",
+      "x-github-event": "pull_request",
+      "x-hub-signature-256": signature,
+    };
+    const context = {
+      req: {
+        raw: request,
+        header(name: string) {
+          return headers[name.toLowerCase()] ?? null;
+        },
+      },
+      env,
+      json(payload: unknown, status?: number) {
+        return Response.json(payload, status === undefined ? undefined : { status });
+      },
+    } as unknown as Context<{ Bindings: Env }>;
+
+    const response = await handleGitHubWebhook(context);
+    expect(response.status).toBe(202);
+    await expect(response.json()).resolves.toMatchObject({ status: "duplicate" });
+    expect(sendCount).toBe(0); // not re-enqueued
+  });
+});
+
 async function signWebhook(body: string, secret: string): Promise<string> {
   const key = await crypto.subtle.importKey("raw", new TextEncoder().encode(secret), { name: "HMAC", hash: "SHA-256" }, false, ["sign"]);
   const signed = await crypto.subtle.sign("HMAC", key, new TextEncoder().encode(body));