diff --git a/clang/include/clang/AST/CanonicalType.h b/clang/include/clang/AST/CanonicalType.h
index 38e6b41977f87b26e5756f73cf5fa71189936c82..99552b36171ee35b463c5fd71c05ee55553f8588 100644
--- a/clang/include/clang/AST/CanonicalType.h
+++ b/clang/include/clang/AST/CanonicalType.h
@@ -16,6 +16,7 @@
 #define LLVM_CLANG_AST_CANONICAL_TYPE_H
 
 #include "clang/AST/Type.h"
+#include "clang/Basic/Diagnostic.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/type_traits.h"
 #include <iterator>