diff --git a/src/rust_mm.rs b/src/rust_mm.rs
index 409fc9f..018d5de 100644
--- a/src/rust_mm.rs
+++ b/src/rust_mm.rs
@@ -1,10 +1,11 @@
 use core::{
     alloc::{GlobalAlloc, Layout},
     ops::BitAnd,
-    ptr::{addr_of_mut, null_mut},
+    ptr::addr_of_mut,
 };
 use nonx_api::nonx_api;
 
+#[repr(align(4096))]
 struct PreInitializeAllocator {
     base: [u128; 1024],
     inited: bool,
@@ -42,7 +43,8 @@ impl PreInitializeAllocator {
             }
         }
         if start == 0 {
-            null_mut()
+            panic!("PreInitializeAllocator runs out. Bit map:\n{:#x}\n{:#x}\n{:#x}\n{:#x}\n{:#x}\n{:#x}\n{:#x}\n{:#x}",
+            self.base[0], self.base[1], self.base[2], self.base[3], self.base[4], self.base[5], self.base[6], self.base[7]);
         } else {
             addr_of_mut!(self.base[start]) as *mut u8
         }