diff --git a/.changeset/fuzzy-trees-fetch.md b/.changeset/fuzzy-trees-fetch.md
new file mode 100644
index 00000000..4cf5c5df
--- /dev/null
+++ b/.changeset/fuzzy-trees-fetch.md
@@ -0,0 +1,5 @@
+---
+"@proofkit/webviewer": patch
+---
+
+Retry fmFetch when FileMaker bridge is briefly unavailable and keep callback-mode dispatch failures catchable.
diff --git a/packages/webviewer/src/main.ts b/packages/webviewer/src/main.ts
index 71ff8812..87c10c8d 100644
--- a/packages/webviewer/src/main.ts
+++ b/packages/webviewer/src/main.ts
@@ -1,6 +1,9 @@
 import { v4 } from "uuid";
 
 let webViewerName: string;
+const FM_FETCH_FILEMAKER_RETRY_DELAYS_MS = [250, 500, 1000] as const;
+const FILEMAKER_UNAVAILABLE_MESSAGE = "'window.FileMaker' was not available";
+
 /**
  * @private
  * set the name of the Web Viewer to use for all fetches
@@ -36,15 +39,15 @@ export function fmFetch(
    * @param cb callback function to call when the script is done
    */
   callback: () => void,
-): void;
+): Promise<void>;
 export function fmFetch(scriptName: string, data: string | object, callback?: () => void) {
   if (callback) {
-    return _execScript(scriptName, data, callback);
+    return _execScriptWithFileMakerRetry(scriptName, data, callback);
   }
-  return new Promise((resolve) => {
-    _execScript(scriptName, data, (result) => {
+  return new Promise((resolve, reject) => {
+    _execScriptWithFileMakerRetry(scriptName, data, (result) => {
       resolve(result);
-    });
+    }).catch(reject);
   });
 }
 
@@ -83,7 +86,37 @@ function _execScript(scriptName: string, data: unknown, cb: (arg0?: unknown) =>
     data,
     callback: { fetchId, fn: "handleFmWVFetchCallback", webViewerName },
   };
-  callFMScript(scriptName, param);
+  try {
+    callFMScript(scriptName, param);
+  } catch (error) {
+    delete cbs[fetchId];
+    throw error;
+  }
+}
+
+function isFileMakerUnavailableError(error: unknown): boolean {
+  return error instanceof Error && error.message.includes(FILEMAKER_UNAVAILABLE_MESSAGE);
+}
+
+function wait(ms: number): Promise<void> {
+  return new Promise((resolve) => {
+    setTimeout(resolve, ms);
+  });
+}
+
+async function _execScriptWithFileMakerRetry(scriptName: string, data: unknown, cb: (arg0?: unknown) => void) {
+  for (let attempt = 0; ; attempt++) {
+    try {
+      _execScript(scriptName, data, cb);
+      return;
+    } catch (error) {
+      const delay = FM_FETCH_FILEMAKER_RETRY_DELAYS_MS[attempt];
+      if (!(delay && isFileMakerUnavailableError(error))) {
+        throw error;
+      }
+      await wait(delay);
+    }
+  }
 }
 
 /**
diff --git a/packages/webviewer/tests/main.test.ts b/packages/webviewer/tests/main.test.ts
new file mode 100644
index 00000000..d7cef887
--- /dev/null
+++ b/packages/webviewer/tests/main.test.ts
@@ -0,0 +1,62 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+describe("fmFetch", () => {
+  const originalWindow = globalThis.window;
+
+  beforeEach(() => {
+    vi.useFakeTimers();
+    vi.resetModules();
+    globalThis.window = {} as Window & typeof globalThis;
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+    if (typeof originalWindow === "undefined") {
+      Reflect.deleteProperty(globalThis, "window");
+    } else {
+      globalThis.window = originalWindow;
+    }
+  });
+
+  it("retries when FileMaker is not yet available", async () => {
+    const { fmFetch } = await import("../src/main.ts");
+    const performScript = vi.fn();
+
+    const result = fmFetch("LoadData", { id: "123" });
+    globalThis.window.FileMaker = {
+      PerformScript: performScript,
+      PerformScriptWithOption: vi.fn(),
+    };
+
+    await vi.advanceTimersByTimeAsync(250);
+
+    expect(performScript).toHaveBeenCalledTimes(1);
+    const params = JSON.parse(String(performScript.mock.calls[0]?.[1])) as {
+      callback: { fetchId: string };
+    };
+    globalThis.window.handleFmWVFetchCallback(JSON.stringify({ ok: true }), params.callback.fetchId);
+    await vi.advanceTimersByTimeAsync(1);
+
+    await expect(result).resolves.toEqual({ ok: true });
+  });
+
+  it("rejects after three FileMaker availability retries", async () => {
+    const { fmFetch } = await import("../src/main.ts");
+
+    const result = fmFetch("LoadData", { id: "123" });
+    const rejection = expect(result).rejects.toThrow("'window.FileMaker' was not available");
+    await vi.advanceTimersByTimeAsync(1750);
+
+    await rejection;
+  });
+
+  it("returns a catchable rejection in callback mode after retries", async () => {
+    const { fmFetch } = await import("../src/main.ts");
+
+    const result = fmFetch("LoadData", { id: "123" }, vi.fn());
+    const rejection = expect(result).rejects.toThrow("'window.FileMaker' was not available");
+    await vi.advanceTimersByTimeAsync(1750);
+
+    await rejection;
+  });
+});