diff --git a/libcxx/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp b/libcxx/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp
--- a/libcxx/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp
@@ -29,38 +29,25 @@
     assert(std::atomic<T>().is_lock_free());
 }
 
-// FIXME: This separate test is needed to work around llvm.org/PR31864
-// which causes ATOMIC_LLONG_LOCK_FREE to be defined as '1' in 32-bit builds
-// even though __atomic_always_lock_free returns true for the same type.
-constexpr bool NeedWorkaroundForPR31864 =
-#if defined(__clang__)
-(sizeof(void*) == 4); // Needed on 32 bit builds
+void checkLongLongTypes() {
+  static_assert(std::atomic<long long>::is_always_lock_free == __atomic_always_lock_free(sizeof(long long), 0), "");
+  static_assert(std::atomic<unsigned long long>::is_always_lock_free ==
+                    __atomic_always_lock_free(sizeof(unsigned long long), 0),
+                "");
+// This looks like a GCC bug, it failed with static_assert, but succeeded with assert.
+#ifdef __GNUC__
+  assert(__atomic_always_lock_free(sizeof(long long), (long long*)alignof(long long)) == (2 == ATOMIC_LLONG_LOCK_FREE));
+  assert(__atomic_always_lock_free(sizeof(unsigned long long), (unsigned long long*)alignof(unsigned long long)) ==
+         (2 == ATOMIC_LLONG_LOCK_FREE));
 #else
-false;
+  static_assert(__atomic_always_lock_free(sizeof(long long), (long long*)alignof(long long)) ==
+                    (2 == ATOMIC_LLONG_LOCK_FREE),
+                "");
+  static_assert(
+      __atomic_always_lock_free(sizeof(unsigned long long), (unsigned long long*)alignof(unsigned long long)) ==
+          (2 == ATOMIC_LLONG_LOCK_FREE),
+      "");
 #endif
-
-template <bool Disable = NeedWorkaroundForPR31864,
-  std::enable_if_t<!Disable>* = nullptr,
-  class LLong = long long,
-  class ULLong = unsigned long long>
-void checkLongLongTypes() {
-  static_assert(std::atomic<LLong>::is_always_lock_free == (2 == ATOMIC_LLONG_LOCK_FREE), "");
-  static_assert(std::atomic<ULLong>::is_always_lock_free == (2 == ATOMIC_LLONG_LOCK_FREE), "");
-}
-
-// Used to make the calls to __atomic_always_lock_free dependent on a template
-// parameter.
-template <class T> constexpr size_t getSizeOf() { return sizeof(T); }
-
-template <bool Enable = NeedWorkaroundForPR31864,
-  std::enable_if_t<Enable>* = nullptr,
-  class LLong = long long,
-  class ULLong = unsigned long long>
-void checkLongLongTypes() {
-  constexpr bool ExpectLockFree = __atomic_always_lock_free(getSizeOf<LLong>(), 0);
-  static_assert(std::atomic<LLong>::is_always_lock_free == ExpectLockFree, "");
-  static_assert(std::atomic<ULLong>::is_always_lock_free == ExpectLockFree, "");
-  static_assert((0 != ATOMIC_LLONG_LOCK_FREE) == ExpectLockFree, "");
 }
 
 void run()