diff --git a/llvm/include/llvm/Support/Format.h b/llvm/include/llvm/Support/Format.h
index 3b93a0f206523..89b6ae35ba5de 100644
--- a/llvm/include/llvm/Support/Format.h
+++ b/llvm/include/llvm/Support/Format.h
@@ -28,6 +28,7 @@
 #include "llvm/Support/DataTypes.h"
 #include <cassert>
 #include <cstdio>
+#include <optional>
 #include <tuple>
 #include <utility>