diff --git a/__tests__/backend/utils/DriveBackedValue.test.ts b/__tests__/backend/utils/DriveBackedValue.test.ts
index 06bbe77f..a9adc4cf 100644
--- a/__tests__/backend/utils/DriveBackedValue.test.ts
+++ b/__tests__/backend/utils/DriveBackedValue.test.ts
@@ -305,10 +305,7 @@ test("DriveBackedValue loads a value - the folder exists, the value exists", ()
     ],
   };
   const driveServiceMock = mockedSafeDriveService();
-  driveServiceMock.Files.get.mockReturnValueOnce(
-    // Incorrect upstream typings, string is actually permissible
-    JSON.stringify("VALUE") as unknown as GoogleAppsScript.Drive.Schema.File,
-  );
+  driveServiceMock.Files.get.mockReturnValueOnce(JSON.stringify("VALUE"));
   driveServiceMock.Files.list
     .mockReturnValueOnce(response1)
     .mockReturnValueOnce(response2);
diff --git a/__tests__/test-utils/gas-stubs.ts b/__tests__/test-utils/gas-stubs.ts
index 391e49a2..95c939d7 100644
--- a/__tests__/test-utils/gas-stubs.ts
+++ b/__tests__/test-utils/gas-stubs.ts
@@ -135,7 +135,18 @@ export function mockedFilesCollection(): GoogleAppsScript.Drive.Collection.Files
     emptyTrash: jest.fn<() => void>(),
     export: jest.fn<(fileId: string, mimeType: string) => void>(),
     generateIds: jest.fn<() => GoogleAppsScript.Drive.Schema.GeneratedIds>(),
-    get: jest.fn<(fileId: string) => GoogleAppsScript.Drive.Schema.File>(),
+    get: jest.fn() as {
+      (
+        fileId: string,
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any -- From upstream types
+        optionalArgs?: Record<string, any> & { alt: "media" },
+      ): string;
+      (
+        fileId: string,
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any -- From upstream types
+        optionalArgs?: Record<string, any>,
+      ): GoogleAppsScript.Drive.Schema.File;
+    },
     insert:
       jest.fn<
         (
diff --git a/package-lock.json b/package-lock.json
index b591f6f7..0f56c4a9 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -22,7 +22,7 @@
         "@smui/linear-progress": "^7.0.0",
         "@smui/list": "^7.0.0",
         "@smui/top-app-bar": "^7.0.0",
-        "@types/google-apps-script": "^1.0.86",
+        "@types/google-apps-script": "^1.0.89",
         "@types/google.script.client-side": "^0.1.5",
         "@types/jest": "^29.5.14",
         "@types/node": "^22.9.3",
@@ -4077,9 +4077,9 @@
       }
     },
     "node_modules/@types/google-apps-script": {
-      "version": "1.0.86",
-      "resolved": "https://registry.npmjs.org/@types/google-apps-script/-/google-apps-script-1.0.86.tgz",
-      "integrity": "sha512-w0tLty8vpApjIp+czorfcoY9k1nZSdQsg6lru3ZV6EWdNyXNsetIZPQnvBIihENAhcGwlogiDKx8z/57NYB3jA==",
+      "version": "1.0.89",
+      "resolved": "https://registry.npmjs.org/@types/google-apps-script/-/google-apps-script-1.0.89.tgz",
+      "integrity": "sha512-Vbvuyno3JnmFDwt4gOLSZKg3/EKLyViVhGqDt1oowY19M1x7Tl1sxOMSnAPdVGH5X/k2pcDWAh+poNaU8Jxwkw==",
       "dev": true,
       "license": "MIT"
     },
diff --git a/package.json b/package.json
index c4430807..29f35ceb 100644
--- a/package.json
+++ b/package.json
@@ -27,7 +27,7 @@
     "@smui/linear-progress": "^7.0.0",
     "@smui/list": "^7.0.0",
     "@smui/top-app-bar": "^7.0.0",
-    "@types/google-apps-script": "^1.0.86",
+    "@types/google-apps-script": "^1.0.89",
     "@types/google.script.client-side": "^0.1.5",
     "@types/jest": "^29.5.14",
     "@types/node": "^22.9.3",