Index: include/lld/Core/Simple.h
===================================================================
--- include/lld/Core/Simple.h
+++ include/lld/Core/Simple.h
@@ -174,7 +174,7 @@
 class SimpleDefinedAtom : public DefinedAtom {
 public:
   explicit SimpleDefinedAtom(const File &f) : _file(f) {
-    static uint32_t lastOrdinal = 0;
+    static std::atomic<uint32_t> lastOrdinal;
     _ordinal = lastOrdinal++;
     _references.setAllocator(&f.allocator());
   }