diff --git a/apps/desktop/src/features/score/scoreStorage.test.ts b/apps/desktop/src/features/score/scoreStorage.test.ts
index 0feec199..c039e5bd 100644
--- a/apps/desktop/src/features/score/scoreStorage.test.ts
+++ b/apps/desktop/src/features/score/scoreStorage.test.ts
@@ -16,6 +16,47 @@ describe("scoreStorage bridge resolution", () => {
     delete tauriWindow.__TAURI_INVOKE__;
   });
 
+  it("throws INVALID_RESPONSE_MESSAGE when readScorePdf returns an array with non-number elements (early exit)", async () => {
+    const mockInvoke = vi.fn().mockResolvedValue([1, 2, "not-a-number", 4]);
+    const tauriWindow = {
+      __TAURI_INVOKE__: mockInvoke
+    } as unknown as TauriWindow;
+    vi.stubGlobal("window", tauriWindow);
+
+    await expect(readScorePdf("project-1", "score-1")).rejects.toThrow("Invalid score bridge response");
+    expect(mockInvoke).toHaveBeenCalledWith("read_score_pdf", { projectId: "project-1", scoreId: "score-1" });
+  });
+
+  it.each([
+    ["negative", -1],
+    ["above the byte range", 256],
+    ["fractional", 1.5],
+    ["NaN", Number.NaN],
+    ["infinite", Number.POSITIVE_INFINITY]
+  ])("rejects %s numeric values before Uint8Array coercion", async (_label, invalidByte) => {
+    const mockInvoke = vi.fn().mockResolvedValue([0, invalidByte, 255]);
+    const tauriWindow = {
+      __TAURI_INVOKE__: mockInvoke
+    } as unknown as TauriWindow;
+    vi.stubGlobal("window", tauriWindow);
+
+    await expect(readScorePdf("project-1", "score-1")).rejects.toThrow("Invalid score bridge response");
+    expect(mockInvoke).toHaveBeenCalledWith("read_score_pdf", { projectId: "project-1", scoreId: "score-1" });
+  });
+
+  it("returns Uint8Array when readScorePdf returns a valid number array", async () => {
+    const mockInvoke = vi.fn().mockResolvedValue([1, 2, 3, 4]);
+    const tauriWindow = {
+      __TAURI_INVOKE__: mockInvoke
+    } as unknown as TauriWindow;
+    vi.stubGlobal("window", tauriWindow);
+
+    const result = await readScorePdf("project-1", "score-1");
+    expect(result).toBeInstanceOf(Uint8Array);
+    expect(result).toEqual(new Uint8Array([1, 2, 3, 4]));
+    expect(mockInvoke).toHaveBeenCalledWith("read_score_pdf", { projectId: "project-1", scoreId: "score-1" });
+  });
+
   it("fails closed on every command when there is no window (non-browser runtime)", async () => {
     // Simulate a runtime without a DOM window (e.g. SSR / bundler prerender):
     // getInvoke() must take the `typeof window === "undefined"` branch and
diff --git a/apps/desktop/src/features/score/scoreStorage.ts b/apps/desktop/src/features/score/scoreStorage.ts
index 492f1259..e9bd8990 100644
--- a/apps/desktop/src/features/score/scoreStorage.ts
+++ b/apps/desktop/src/features/score/scoreStorage.ts
@@ -91,7 +91,18 @@ export async function readScorePdf(projectId: string, scoreId: string): Promise<
   if (response instanceof ArrayBuffer) {
     return new Uint8Array(response);
   }
-  if (Array.isArray(response) && response.every((byte) => typeof byte === "number")) {
+  if (Array.isArray(response)) {
+    for (let index = 0; index < response.length; index += 1) {
+      const byte = response[index];
+      if (
+        typeof byte !== "number" ||
+        !Number.isInteger(byte) ||
+        byte < 0 ||
+        byte > 255
+      ) {
+        throw new Error(INVALID_RESPONSE_MESSAGE);
+      }
+    }
     return Uint8Array.from(response as number[]);
   }