diff --git a/include/llvm/ADT/OwningPtr.h b/include/llvm/ADT/OwningPtr.h
index 7007d25a41b..95d7db17b91 100644
--- a/include/llvm/ADT/OwningPtr.h
+++ b/include/llvm/ADT/OwningPtr.h
@@ -15,6 +15,7 @@
 #define LLVM_ADT_OWNING_PTR_H
 
 #include <cassert>
+#include <cstddef>
 
 namespace llvm {