diff --git a/kernel/src/syscall/mmap.rs b/kernel/src/syscall/mmap.rs
index a25633cc2..bea99c046 100644
--- a/kernel/src/syscall/mmap.rs
+++ b/kernel/src/syscall/mmap.rs
@@ -24,7 +24,7 @@ pub fn sys_mmap(
     offset: u64,
     ctx: &Context,
 ) -> Result<SyscallReturn> {
-    let perms = VmPerms::from_posix_prot_bits(perms as u32).unwrap();
+    let perms = VmPerms::from_bits_truncate(perms as u32);
     let option = MMapOptions::try_from(flags as u32)?;
     let res = do_sys_mmap(
         addr as usize,
diff --git a/kernel/src/vm/perms.rs b/kernel/src/vm/perms.rs
index 8a3cbb14b..15b959b86 100644
--- a/kernel/src/vm/perms.rs
+++ b/kernel/src/vm/perms.rs
@@ -16,12 +16,6 @@ bitflags! {
     }
 }
 
-impl VmPerms {
-    pub fn from_posix_prot_bits(bits: u32) -> Option<Self> {
-        VmPerms::from_bits(bits)
-    }
-}
-
 impl From<Rights> for VmPerms {
     fn from(rights: Rights) -> VmPerms {
         let mut vm_perm = VmPerms::empty();