diff --git a/.changeset/clean-cats-study.md b/.changeset/clean-cats-study.md
new file mode 100644
index 0000000000..5345e15abb
--- /dev/null
+++ b/.changeset/clean-cats-study.md
@@ -0,0 +1,5 @@
+---
+"@definitelytyped/utils": patch
+---
+
+Handle non-OK status codes in getUrlContentsAsString
diff --git a/packages/utils/src/io.ts b/packages/utils/src/io.ts
index 0574ae5981..7b8d374de9 100644
--- a/packages/utils/src/io.ts
+++ b/packages/utils/src/io.ts
@@ -314,6 +314,11 @@ function getUrlContentsAsString(url: string): Promise<string> {
         let data = "";
         res.on("data", (d) => (data += d));
         res.on("end", () => {
+          const statusCode = res.statusCode ?? 0;
+          if (statusCode < 200 || statusCode >= 300) {
+            reject(new Error(`Request to ${url} failed with status code ${statusCode}: ${data}`));
+            return;
+          }
           resolve(data);
         });
       })
diff --git a/packages/utils/test/io.test.ts b/packages/utils/test/io.test.ts
index 3b181828e0..f006d9da7c 100644
--- a/packages/utils/test/io.test.ts
+++ b/packages/utils/test/io.test.ts
@@ -1,9 +1,62 @@
 import path from "path";
 import fs from "fs";
+import os from "os";
+import https from "https";
+import { EventEmitter } from "events";
 import { list } from "tar";
-import { createTgz } from "../src/io";
+import { createTgz, createGitHubStringSetGetter } from "../src/io";
 
 describe("io", () => {
+  describe(createGitHubStringSetGetter, () => {
+    const originalNodeEnv = process.env.NODE_ENV;
+    let fallbackPath: string;
+    let getSpy: jest.SpyInstance;
+
+    beforeEach(() => {
+      // Force the network path (skipped when NODE_ENV === "test").
+      process.env.NODE_ENV = "production";
+      fallbackPath = path.join(os.tmpdir(), `gh-string-set-getter-${Date.now()}.txt`);
+      fs.writeFileSync(fallbackPath, "local-a\nlocal-b\n");
+    });
+
+    afterEach(() => {
+      process.env.NODE_ENV = originalNodeEnv;
+      getSpy?.mockRestore();
+      if (fs.existsSync(fallbackPath)) {
+        fs.unlinkSync(fallbackPath);
+      }
+    });
+
+    function mockHttpsGet(statusCode: number, body: string): void {
+      getSpy = jest.spyOn(https, "get").mockImplementation(((_url: unknown, cb: (res: unknown) => void) => {
+        const res = new EventEmitter() as EventEmitter & { statusCode: number };
+        res.statusCode = statusCode;
+        process.nextTick(() => {
+          res.emit("data", body);
+          res.emit("end");
+        });
+        cb(res);
+        return new EventEmitter();
+      }) as unknown as typeof https.get);
+    }
+
+    it("falls back to the local copy when GitHub responds with a non-2xx status", async () => {
+      // Regression test: a rate-limited/errored response body must not be parsed as the file.
+      mockHttpsGet(429, "429: Too Many Requests\nrate limit exceeded");
+      const getter = createGitHubStringSetGetter("some/path.txt", fallbackPath);
+      const result = await getter();
+      expect(result).toEqual(new Set(["local-a", "local-b", ""]));
+      expect(result.has("429: Too Many Requests")).toBe(false);
+    });
+
+    it("uses the fetched contents when GitHub responds with 200", async () => {
+      mockHttpsGet(200, "remote-a\nremote-b\n");
+      const getter = createGitHubStringSetGetter("some/path.txt", fallbackPath);
+      const result = await getter();
+      expect(result).toEqual(new Set(["remote-a", "remote-b", ""]));
+    });
+  });
+
   describe(createTgz, () => {
     it("packs a directory", (done) => {
       const dir = path.join(__dirname, "data", "pack");