diff --git a/libc/src/__support/CPP/atomic.h b/libc/src/__support/CPP/atomic.h
--- a/libc/src/__support/CPP/atomic.h
+++ b/libc/src/__support/CPP/atomic.h
@@ -92,6 +92,11 @@
   void set(T rhs) { val = rhs; }
 };
 
+// Issue a thread fence with the given memory ordering.
+LIBC_INLINE void atomic_thread_fence(MemoryOrder mem_ord) {
+  __atomic_thread_fence(int(mem_ord));
+}
+
 } // namespace cpp
 } // namespace __llvm_libc