diff --git a/include/typeinfo b/include/typeinfo
index 5d2f03e..2760176 100644
--- a/include/typeinfo
+++ b/include/typeinfo
@@ -237,7 +237,10 @@
     }
 
    private:
-    typedef std::integral_constant<__type_name_t, (1ULL << 63)> __non_unique_rtti_bit;
+    // The unique bit is the top bit. It is expected that __type_name_t is 64 bits when
+    // this implementation is actually used.
+    typedef std::integral_constant<__type_name_t,
+      (1ULL << ((__CHAR_BIT__ * sizeof(__type_name_t)) - 1))> __non_unique_rtti_bit;
 
     _LIBCPP_INLINE_VISIBILITY
     static bool __is_type_name_unique(__type_name_t __lhs) _NOEXCEPT {