diff --git a/os/src/mm/page_table.rs b/os/src/mm/page_table.rs
index d1bc645f..0ce485ce 100644
--- a/os/src/mm/page_table.rs
+++ b/os/src/mm/page_table.rs
@@ -102,12 +102,12 @@ impl PageTable {
         }
         result
     }
-    fn find_pte(&self, vpn: VirtPageNum) -> Option<&PageTableEntry> {
+    fn find_pte(&self, vpn: VirtPageNum) -> Option<&mut PageTableEntry> {
         let idxs = vpn.indexes();
         let mut ppn = self.root_ppn;
-        let mut result: Option<&PageTableEntry> = None;
+        let mut result: Option<&mut PageTableEntry> = None;
         for i in 0..3 {
-            let pte = &ppn.get_pte_array()[idxs[i]];
+            let pte = &mut ppn.get_pte_array()[idxs[i]];
             if i == 2 {
                 result = Some(pte);
                 break;
@@ -127,7 +127,7 @@ impl PageTable {
     }
     #[allow(unused)]
     pub fn unmap(&mut self, vpn: VirtPageNum) {
-        let pte = self.find_pte_create(vpn).unwrap();
+        let pte = self.find_pte(vpn).unwrap();
         assert!(pte.is_valid(), "vpn {:?} is invalid before unmapping", vpn);
         *pte = PageTableEntry::empty();
     }