diff --git a/kernel/src/syscall/dup.rs b/kernel/src/syscall/dup.rs
index 24d9cb9d4..833a133a4 100644
--- a/kernel/src/syscall/dup.rs
+++ b/kernel/src/syscall/dup.rs
@@ -56,12 +56,12 @@ fn do_dup3(
         return_errno!(Errno::EINVAL);
     }
 
-    if new_fd
+    if new_fd.cast_unsigned() as u64
         >= ctx
             .process
             .resource_limits()
             .get_rlimit(ResourceType::RLIMIT_NOFILE)
-            .get_cur() as FileDesc
+            .get_cur()
     {
         return_errno!(Errno::EBADF);
     }