diff --git a/os/src/mm/address.rs b/os/src/mm/address.rs
index dd25b636..90ec3aaa 100644
--- a/os/src/mm/address.rs
+++ b/os/src/mm/address.rs
@@ -69,7 +69,7 @@ impl From<VirtPageNum> for usize {
 
 impl VirtAddr {
     pub fn floor(&self) -> VirtPageNum { VirtPageNum(self.0 / PAGE_SIZE) }
-    pub fn ceil(&self) -> VirtPageNum  { VirtPageNum((self.0 + PAGE_SIZE - 1) / PAGE_SIZE) }
+    pub fn ceil(&self) -> VirtPageNum  { VirtPageNum((self.0 - 1 + PAGE_SIZE) / PAGE_SIZE) }
     pub fn page_offset(&self) -> usize { self.0 & (PAGE_SIZE - 1) }
     pub fn aligned(&self) -> bool { self.page_offset() == 0 }
 }
@@ -84,7 +84,7 @@ impl From<VirtPageNum> for VirtAddr {
 }
 impl PhysAddr {
     pub fn floor(&self) -> PhysPageNum { PhysPageNum(self.0 / PAGE_SIZE) }
-    pub fn ceil(&self) -> PhysPageNum { PhysPageNum((self.0 + PAGE_SIZE - 1) / PAGE_SIZE) }
+    pub fn ceil(&self) -> PhysPageNum { PhysPageNum((self.0 - 1 + PAGE_SIZE) / PAGE_SIZE) }
     pub fn page_offset(&self) -> usize { self.0 & (PAGE_SIZE - 1) }
     pub fn aligned(&self) -> bool { self.page_offset() == 0 }
 }