diff --git a/os/src/mm/address.rs b/os/src/mm/address.rs
index cf147a08..df3e130f 100644
--- a/os/src/mm/address.rs
+++ b/os/src/mm/address.rs
@@ -101,7 +101,11 @@ impl VirtAddr {
         VirtPageNum(self.0 / PAGE_SIZE)
     }
     pub fn ceil(&self) -> VirtPageNum {
-        VirtPageNum((self.0 - 1 + PAGE_SIZE) / PAGE_SIZE)
+        if self.0 == 0 {
+            VirtPageNum(0)
+        } else {
+            VirtPageNum((self.0 - 1 + PAGE_SIZE) / PAGE_SIZE)
+        }
     }
     pub fn page_offset(&self) -> usize {
         self.0 & (PAGE_SIZE - 1)
@@ -126,7 +130,11 @@ impl PhysAddr {
         PhysPageNum(self.0 / PAGE_SIZE)
     }
     pub fn ceil(&self) -> PhysPageNum {
-        PhysPageNum((self.0 - 1 + PAGE_SIZE) / PAGE_SIZE)
+        if self.0 == 0 {
+            PhysPageNum(0)
+        } else {
+            PhysPageNum((self.0 - 1 + PAGE_SIZE) / PAGE_SIZE)
+        }
     }
     pub fn page_offset(&self) -> usize {
         self.0 & (PAGE_SIZE - 1)