diff --git a/compiler-rt/lib/builtins/atomic.c b/compiler-rt/lib/builtins/atomic.c
--- a/compiler-rt/lib/builtins/atomic.c
+++ b/compiler-rt/lib/builtins/atomic.c
@@ -120,14 +120,12 @@
   return locks + (hash & SPINLOCK_MASK);
 }
 
-/// Macros for determining whether a size is lock free.  Clang can not yet
-/// codegen __atomic_is_lock_free(16), so for now we assume 16-byte values are
-/// not lock free.
-#define IS_LOCK_FREE_1 __c11_atomic_is_lock_free(1)
-#define IS_LOCK_FREE_2 __c11_atomic_is_lock_free(2)
-#define IS_LOCK_FREE_4 __c11_atomic_is_lock_free(4)
-#define IS_LOCK_FREE_8 __c11_atomic_is_lock_free(8)
-#define IS_LOCK_FREE_16 0
+/// Macros for determining whether a size is lock free.
+#define IS_LOCK_FREE_1 __atomic_always_lock_free(1, NULL)
+#define IS_LOCK_FREE_2 __atomic_always_lock_free(2, NULL)
+#define IS_LOCK_FREE_4 __atomic_always_lock_free(4, NULL)
+#define IS_LOCK_FREE_8 __atomic_always_lock_free(8, NULL)
+#define IS_LOCK_FREE_16 __atomic_always_lock_free(16, NULL)
 
 /// Macro that calls the compiler-generated lock-free versions of functions
 /// when they exist.