diff --git a/include/llvm/ADT/PointerUnion.h b/include/llvm/ADT/PointerUnion.h
index b63ee52cddd..c1a6d744128 100644
--- a/include/llvm/ADT/PointerUnion.h
+++ b/include/llvm/ADT/PointerUnion.h
@@ -15,6 +15,7 @@
 #ifndef LLVM_ADT_POINTERUNION_H
 #define LLVM_ADT_POINTERUNION_H
 
+#include "llvm/Support/Compiler.h"
 #include "llvm/ADT/PointerIntPair.h"
 
 namespace llvm {