diff --git a/kernel/src/objects/cnode.rs b/kernel/src/objects/cnode.rs
index d8668c9..fd4303a 100644
--- a/kernel/src/objects/cnode.rs
+++ b/kernel/src/objects/cnode.rs
@@ -108,7 +108,8 @@ impl<'a> CNodeCap<'a> {
                 });
             }
 
-            let get_guard = || (cap_ptr >> (bits_remaining - guard_bits)) & MASK!(guard_bits);
+            let get_guard =
+                || cap_ptr.checked_shr((bits_remaining - guard_bits) as u32).unwrap_or_default() & MASK!(guard_bits);
             if guard_bits > bits_remaining || get_guard() != cap_guard {
                 return Err(LookupFailure::GuardMismatch {
                     bits_left:   bits_remaining,