diff --git a/test/syscalls/linux/fork.cc b/test/syscalls/linux/fork.cc
index 2f751c974..93df86199 100644
--- a/test/syscalls/linux/fork.cc
+++ b/test/syscalls/linux/fork.cc
@@ -437,7 +437,7 @@ TEST(CloneTest, NewUserNamespacePermitsAllOtherNamespaces) {
 
 // Clone with CLONE_SETTLS and a non-canonical TLS address is rejected.
 TEST(CloneTest, NonCanonicalTLS) {
-  constexpr uintptr_t kNonCanonical = 1ull << 48;
+  constexpr uintptr_t kNonCanonical = 1ull << 63;
 
   // We need a valid address for the stack pointer. We'll never actually execute
   // on this.