diff --git a/llvm/unittests/ADT/OptionalTest.cpp b/llvm/unittests/ADT/OptionalTest.cpp
index 8d49b3dc22ac..c39b6727cd54 100644
--- a/llvm/unittests/ADT/OptionalTest.cpp
+++ b/llvm/unittests/ADT/OptionalTest.cpp
@@ -12,6 +12,8 @@
 #include "gtest/gtest-spi.h"
 #include "gtest/gtest.h"
 
+#include <array>
+
 using namespace llvm;
 
 namespace {