diff --git a/include/memory b/include/memory
index c7f540b..8ef4588 100644
--- a/include/memory
+++ b/include/memory
@@ -3037,7 +3037,7 @@
     typedef unique_ptr<_Tp, _Dp> argument_type;
     typedef size_t               result_type;
     _LIBCPP_INLINE_VISIBILITY
-    result_type operator()(const argument_type& __ptr) const _NOEXCEPT
+    result_type operator()(const argument_type& __ptr) const
     {
         typedef typename argument_type::pointer pointer;
         return hash<pointer>()(__ptr.get());
diff --git a/include/optional b/include/optional
index 180f63f..002842f 100644
--- a/include/optional
+++ b/include/optional
@@ -1301,7 +1301,7 @@
     typedef size_t        result_type;
 
     _LIBCPP_INLINE_VISIBILITY
-    result_type operator()(const argument_type& __opt) const _NOEXCEPT
+    result_type operator()(const argument_type& __opt) const
     {
         return static_cast<bool>(__opt) ? hash<remove_const_t<_Tp>>()(*__opt) : 0;
     }
diff --git a/include/thread b/include/thread
index 94c77e0..874ce3e 100644
--- a/include/thread
+++ b/include/thread
@@ -261,7 +261,7 @@
     : public unary_function<__thread_id, size_t>
 {
     _LIBCPP_INLINE_VISIBILITY
-    size_t operator()(__thread_id __v) const
+    size_t operator()(__thread_id __v) const _NOEXCEPT
     {
         return hash<__libcpp_thread_id>()(__v.__id_);
     }
diff --git a/include/variant b/include/variant
index 099e6c3..33f88e0 100644
--- a/include/variant
+++ b/include/variant
@@ -1562,7 +1562,7 @@
   using result_type = size_t;
 
   inline _LIBCPP_INLINE_VISIBILITY
-  result_type operator()(const argument_type&) const {
+  result_type operator()(const argument_type&) const _NOEXCEPT {
     return 66740831; // return a fundamentally attractive random value.
   }
 };