diff --git a/src/app/api/referrals/route.test.ts b/src/app/api/referrals/route.test.ts
index 3af21063..267f2640 100644
--- a/src/app/api/referrals/route.test.ts
+++ b/src/app/api/referrals/route.test.ts
@@ -254,4 +254,43 @@ describe("POST /api/referrals", () => {
     const body = await res.json();
     expect(body.error).toContain("No valid email");
   });
+
+  // --- Regression tests for #141: reject non-string email entries ---
+
+  it("should return 400 for non-string email entries (e.g. number in array)", async () => {
+    mockGetAuthContext.mockResolvedValue({
+      user: { id: "user1" },
+      supabase: mockSupabase,
+    });
+
+    // Mixed array: valid string + number
+    const res = await POST(makePostRequest({ emails: ["friend@test.com", 42] }));
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toBe("All email entries must be strings");
+  });
+
+  it("should return 400 for null in email array", async () => {
+    mockGetAuthContext.mockResolvedValue({
+      user: { id: "user1" },
+      supabase: mockSupabase,
+    });
+
+    const res = await POST(makePostRequest({ emails: [null] }));
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toBe("All email entries must be strings");
+  });
+
+  it("should return 400 for object in email array", async () => {
+    mockGetAuthContext.mockResolvedValue({
+      user: { id: "user1" },
+      supabase: mockSupabase,
+    });
+
+    const res = await POST(makePostRequest({ emails: [{ email: "test@test.com" }] }));
+    expect(res.status).toBe(400);
+    const body = await res.json();
+    expect(body.error).toBe("All email entries must be strings");
+  });
 });
diff --git a/src/app/api/referrals/route.ts b/src/app/api/referrals/route.ts
index 50099975..0e577e9c 100644
--- a/src/app/api/referrals/route.ts
+++ b/src/app/api/referrals/route.ts
@@ -62,6 +62,13 @@ export async function POST(request: NextRequest) {
       );
     }
 
+    if (!emails.every((email: unknown) => typeof email === "string")) {
+      return NextResponse.json(
+        { error: "All email entries must be strings" },
+        { status: 400 }
+      );
+    }
+
     if (emails.length > 20) {
       return NextResponse.json(
         { error: "Maximum 20 invites at a time" },