diff --git a/folly/Traits.h b/folly/Traits.h
index 121f12eb413..4035e22eba0 100644
--- a/folly/Traits.h
+++ b/folly/Traits.h
@@ -196,8 +196,8 @@ struct is_constexpr_default_constructible_ {
   static std::true_type sfinae(T*);
   static std::false_type sfinae(void*);
   template <typename T>
-  static constexpr bool apply = sizeof(T) &&
-      decltype(sfinae(static_cast<T*>(nullptr)))::value;
+  static constexpr bool apply =
+      !require_sizeof<T> || decltype(sfinae(static_cast<T*>(nullptr)))::value;
 };
 
 } // namespace detail
@@ -405,7 +405,7 @@ struct detected_<void_t<T<A...>>, D, T, A...> {
 //
 //  mimic: std::experimental::detected_or, Library Fundamentals TS v2
 //
-//  Note: not resilient agaist incomplete types; may violate ODR.
+//  Note: not resilient against incomplete types; may violate ODR.
 template <typename D, template <typename...> class T, typename... A>
 using detected_or = detail::detected_<void, D, T, A...>;
 
@@ -418,7 +418,7 @@ using detected_or = detail::detected_<void, D, T, A...>;
 //
 //  mimic: std::experimental::detected_or_t, Library Fundamentals TS v2
 //
-//  Note: not resilient agaist incomplete types; may violate ODR.
+//  Note: not resilient against incomplete types; may violate ODR.
 template <typename D, template <typename...> class T, typename... A>
 using detected_or_t = typename detected_or<D, T, A...>::type;
 
@@ -431,7 +431,7 @@ using detected_or_t = typename detected_or<D, T, A...>::type;
 //
 //  mimic: std::experimental::detected_t, Library Fundamentals TS v2
 //
-//  Note: not resilient agaist incomplete types; may violate ODR.
+//  Note: not resilient against incomplete types; may violate ODR.
 template <template <typename...> class T, typename... A>
 using detected_t = detected_or_t<nonesuch, T, A...>;
 
@@ -449,7 +449,7 @@ using detected_t = detected_or_t<nonesuch, T, A...>;
 //  mimic: std::experimental::is_detected, std::experimental::is_detected_v,
 //    Library Fundamentals TS v2
 //
-//  Note: not resilient agaist incomplete types; may violate ODR.
+//  Note: not resilient against incomplete types; may violate ODR.
 //
 //  Note: the trait type is_detected differs here by being deferred.
 template <template <typename...> class T, typename... A>
@@ -635,7 +635,8 @@ struct IsNothrowSwappable
 template <class T>
 struct IsRelocatable
     : std::conditional<
-          sizeof(T) && is_detected_v<traits_detail::detect_IsRelocatable, T>,
+          !require_sizeof<T> ||
+              is_detected_v<traits_detail::detect_IsRelocatable, T>,
           traits_detail::has_true_IsRelocatable<T>,
           // TODO add this line (and some tests for it) when we
           // upgrade to gcc 4.7
@@ -645,7 +646,7 @@ struct IsRelocatable
 template <class T>
 struct IsZeroInitializable
     : std::conditional<
-          sizeof(T) &&
+          !require_sizeof<T> ||
               is_detected_v<traits_detail::detect_IsZeroInitializable, T>,
           traits_detail::has_true_IsZeroInitializable<T>,
           bool_constant< //
@@ -734,7 +735,7 @@ struct is_transparent : bool_constant<is_transparent_v<T>> {};
 namespace detail {
 
 template <typename T, typename = void>
-FOLLY_INLINE_VARIABLE constexpr bool is_allocator_ = !sizeof(T);
+FOLLY_INLINE_VARIABLE constexpr bool is_allocator_ = !require_sizeof<T>;
 template <typename T>
 FOLLY_INLINE_VARIABLE constexpr bool is_allocator_<
     T,
diff --git a/folly/container/Foreach-inl.h b/folly/container/Foreach-inl.h
index 23a19a6b68b..1c5a0f1d395 100644
--- a/folly/container/Foreach-inl.h
+++ b/folly/container/Foreach-inl.h
@@ -57,7 +57,7 @@ template <typename T>
 using EnableIfMemberGetFound =
     void_t<decltype(std::declval<T>().template get<0>())>;
 template <typename, typename T>
-struct IsMemberGetFound : bool_constant<!sizeof(T)> {};
+struct IsMemberGetFound : bool_constant<!require_sizeof<T>> {};
 template <typename T>
 struct IsMemberGetFound<EnableIfMemberGetFound<T>, T> : std::true_type {};
 
@@ -91,7 +91,7 @@ using EnableIfTuple = void_t<
     decltype(get_impl<0>(std::declval<T>())),
     decltype(std::tuple_size<T>::value)>;
 template <typename, typename T>
-struct IsTuple : bool_constant<!sizeof(T)> {};
+struct IsTuple : bool_constant<!require_sizeof<T>> {};
 template <typename T>
 struct IsTuple<EnableIfTuple<T>, T> : std::true_type {};
 
@@ -103,7 +103,7 @@ using EnableIfRange = void_t<
     decltype(access::begin(std::declval<T&>())),
     decltype(access::end(std::declval<T&>()))>;
 template <typename, typename T>
-struct IsRange : bool_constant<!sizeof(T)> {};
+struct IsRange : bool_constant<!require_sizeof<T>> {};
 template <typename T>
 struct IsRange<EnableIfRange<T>, T> : std::true_type {};
 
diff --git a/folly/container/Iterator.h b/folly/container/Iterator.h
index 2e8e8673867..f30b60fb2e5 100644
--- a/folly/container/Iterator.h
+++ b/folly/container/Iterator.h
@@ -36,7 +36,7 @@ namespace folly {
 //  the distance without advancing the iterators or copies of them.
 template <typename Iter, typename SentinelIter>
 FOLLY_INLINE_VARIABLE constexpr bool iterator_has_known_distance_v =
-    !sizeof(Iter) && !sizeof(SentinelIter);
+    !require_sizeof<Iter> || !require_sizeof<SentinelIter>;
 template <typename Iter>
 FOLLY_INLINE_VARIABLE constexpr bool iterator_has_known_distance_v<Iter, Iter> =
     std::is_base_of<
@@ -85,7 +85,7 @@ namespace detail {
 
 template <typename Iter, typename Category, typename = void>
 FOLLY_INLINE_VARIABLE constexpr bool iterator_category_matches_v_ =
-    !sizeof(Iter) && !sizeof(Category);
+    !require_sizeof<Iter> || !require_sizeof<Category>;
 template <typename Iter, typename Category>
 FOLLY_INLINE_VARIABLE constexpr bool iterator_category_matches_v_<
     Iter,
diff --git a/folly/container/detail/F14Policy.h b/folly/container/detail/F14Policy.h
index 17070110bd9..7c8402f87bd 100644
--- a/folly/container/detail/F14Policy.h
+++ b/folly/container/detail/F14Policy.h
@@ -157,7 +157,7 @@ struct FOLLY_MSVC_DECLSPEC(empty_bases) BasePolicy
   // Detection for folly_assume_32bit_hash
 
   template <typename Hasher, typename Void = void>
-  struct ShouldAssume32BitHash : bool_constant<!sizeof(Hasher)> {};
+  struct ShouldAssume32BitHash : bool_constant<!require_sizeof<Hasher>> {};
 
   template <typename Hasher>
   struct ShouldAssume32BitHash<
diff --git a/folly/container/detail/F14Table.h b/folly/container/detail/F14Table.h
index 4507e4506dc..7dcb10d8e74 100644
--- a/folly/container/detail/F14Table.h
+++ b/folly/container/detail/F14Table.h
@@ -154,7 +154,7 @@ struct StdNodeReplica {
 #else
 
 template <typename H>
-struct StdIsFastHash : bool_constant<!!sizeof(H)> {};
+struct StdIsFastHash : std::true_type {};
 template <>
 struct StdIsFastHash<std::hash<long double>> : std::false_type {};
 template <typename... Args>
diff --git a/folly/detail/PolyDetail.h b/folly/detail/PolyDetail.h
index 5c82be64597..b69d956c2c5 100644
--- a/folly/detail/PolyDetail.h
+++ b/folly/detail/PolyDetail.h
@@ -923,7 +923,7 @@ struct ModelsInterfaceFalse0_;
 template <>
 struct ModelsInterfaceFalse0_<false> {
   template <typename... T>
-  using apply = bool_constant<(!sizeof(T) || ...)>;
+  using apply = bool_constant<(!require_sizeof<T> || ...)>;
 };
 template <>
 struct ModelsInterfaceFalse0_<true> {
diff --git a/folly/experimental/coro/Traits.h b/folly/experimental/coro/Traits.h
index 645d1f37c85..7e1b5447e35 100644
--- a/folly/experimental/coro/Traits.h
+++ b/folly/experimental/coro/Traits.h
@@ -69,7 +69,7 @@ inline constexpr bool is_coroutine_handle_v =
 /// implementations have particular requirements on the promise (eg. the
 /// stack-aware awaiters may require the .getAsyncFrame() method)
 template <typename T, typename = void>
-struct is_awaiter : bool_constant<!sizeof(T)> {};
+struct is_awaiter : bool_constant<!require_sizeof<T>> {};
 
 template <typename T>
 struct is_awaiter<T, std::enable_if_t<std::is_void_v<T>>> : std::false_type {};
@@ -88,7 +88,8 @@ constexpr bool is_awaiter_v = is_awaiter<T>::value;
 namespace detail {
 
 template <typename Awaitable, typename = void>
-struct _has_member_operator_co_await : bool_constant<!sizeof(Awaitable)> {};
+struct _has_member_operator_co_await
+    : bool_constant<!require_sizeof<Awaitable>> {};
 
 template <typename T>
 struct _has_member_operator_co_await<T, std::enable_if_t<std::is_void_v<T>>>
@@ -101,7 +102,8 @@ struct _has_member_operator_co_await<
     : is_awaiter<decltype(std::declval<Awaitable>().operator co_await())> {};
 
 template <typename Awaitable, typename = void>
-struct _has_free_operator_co_await : bool_constant<!sizeof(Awaitable)> {};
+struct _has_free_operator_co_await : bool_constant<!require_sizeof<Awaitable>> {
+};
 
 template <typename T>
 struct _has_free_operator_co_await<T, std::enable_if_t<std::is_void_v<T>>>
@@ -211,7 +213,7 @@ using await_result_t = typename await_result<Awaitable>::type;
 namespace detail {
 
 template <typename Promise, typename = void>
-constexpr bool promiseHasAsyncFrame_v = !sizeof(Promise);
+constexpr bool promiseHasAsyncFrame_v = !require_sizeof<Promise>;
 
 template <typename Promise>
 constexpr bool promiseHasAsyncFrame_v<
diff --git a/folly/experimental/coro/ViaIfAsync.h b/folly/experimental/coro/ViaIfAsync.h
index 477cb0fd08e..a4c803096b8 100644
--- a/folly/experimental/coro/ViaIfAsync.h
+++ b/folly/experimental/coro/ViaIfAsync.h
@@ -438,7 +438,7 @@ class ViaIfAsyncAwaitable {
 namespace detail {
 
 template <typename SemiAwaitable, typename = void>
-struct HasViaIfAsyncMethod : bool_constant<!sizeof(SemiAwaitable)> {};
+struct HasViaIfAsyncMethod : bool_constant<!require_sizeof<SemiAwaitable>> {};
 
 template <typename SemiAwaitable>
 struct HasViaIfAsyncMethod<
@@ -501,7 +501,7 @@ struct ViaIfAsyncFunction {
 FOLLY_DEFINE_CPO(detail::adl::ViaIfAsyncFunction, co_viaIfAsync)
 
 template <typename T, typename = void>
-struct is_semi_awaitable : bool_constant<!sizeof(T)> {};
+struct is_semi_awaitable : bool_constant<!require_sizeof<T>> {};
 
 template <typename T>
 struct is_semi_awaitable<T, std::enable_if_t<std::is_void_v<T>>>
diff --git a/folly/functional/protocol.h b/folly/functional/protocol.h
index e09aa6ef532..e78674d27a1 100644
--- a/folly/functional/protocol.h
+++ b/folly/functional/protocol.h
@@ -58,7 +58,7 @@ struct match_empty_function_protocol_fn {
 
   template <typename T>
   static constexpr bool cx_matches_v =
-      sizeof(T) && is_detected_v<detect_from_eq_nullptr, T>;
+      require_sizeof<T>&& is_detected_v<detect_from_eq_nullptr, T>;
 
  public:
   template <typename T, std::enable_if_t<!cx_matches_v<T>, int> = 0>
diff --git a/folly/hash/Hash.h b/folly/hash/Hash.h
index d30ea33828a..45314c35c57 100644
--- a/folly/hash/Hash.h
+++ b/folly/hash/Hash.h
@@ -614,7 +614,8 @@ struct IsAvalanchingHasher;
 
 namespace detail {
 template <typename Hasher, typename Void = void>
-struct IsAvalanchingHasherFromMemberType : bool_constant<!sizeof(Hasher)> {};
+struct IsAvalanchingHasherFromMemberType
+    : bool_constant<!require_sizeof<Hasher>> {};
 
 template <typename Hasher>
 struct IsAvalanchingHasherFromMemberType<