diff --git a/csrc/cpu/cpu_attn_impl.hpp b/csrc/cpu/cpu_attn_impl.hpp
index 5de8a114b2b55..344296528b652 100644
--- a/csrc/cpu/cpu_attn_impl.hpp
+++ b/csrc/cpu/cpu_attn_impl.hpp
@@ -754,7 +754,7 @@ class AttentionScheduler {
         return l2_cache_size >> 1;  // use 50% of L2 cache
       }
       // Fallback if sysctlbyname fails
-      return 128 * 1024 >> 1;  // use 50% of 128KB
+      return 128LL * 1024 >> 1;  // use 50% of 128KB
 #else
       long l2_cache_size = sysconf(_SC_LEVEL2_CACHE_SIZE);
       TORCH_CHECK_NE(l2_cache_size, -1);