diff --git a/kvm-all.c b/kvm-all.c
index fd1fbfec7a055d340767d4a67c93dfedd92d5460..8b85029de366afa74602406d7e61e3e486ea8d14 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -373,7 +373,20 @@ static int kvm_physical_sync_dirty_bitmap(target_phys_addr_t start_addr,
             break;
         }
 
-        size = ALIGN(((mem->memory_size) >> TARGET_PAGE_BITS), HOST_LONG_BITS) / 8;
+        /* XXX bad kernel interface alert
+         * For dirty bitmap, kernel allocates array of size aligned to
+         * bits-per-long.  But for case when the kernel is 64bits and
+         * the userspace is 32bits, userspace can't align to the same
+         * bits-per-long, since sizeof(long) is different between kernel
+         * and user space.  This way, userspace will provide buffer which
+         * may be 4 bytes less than the kernel will use, resulting in
+         * userspace memory corruption (which is not detectable by valgrind
+         * too, in most cases).
+         * So for now, let's align to 64 instead of HOST_LONG_BITS here, in
+         * a hope that sizeof(long) wont become >8 any time soon.
+         */
+        size = ALIGN(((mem->memory_size) >> TARGET_PAGE_BITS),
+                     /*HOST_LONG_BITS*/ 64) / 8;
         if (!d.dirty_bitmap) {
             d.dirty_bitmap = qemu_malloc(size);
         } else if (size > allocated_size) {