diff --git a/llvm/include/llvm/Support/ItaniumManglingCanonicalizer.h b/llvm/include/llvm/Support/ItaniumManglingCanonicalizer.h
index 6920000340d4f..8774b9e4dbb0e 100644
--- a/llvm/include/llvm/Support/ItaniumManglingCanonicalizer.h
+++ b/llvm/include/llvm/Support/ItaniumManglingCanonicalizer.h
@@ -14,11 +14,12 @@
 #ifndef LLVM_SUPPORT_ITANIUMMANGLINGCANONICALIZER_H
 #define LLVM_SUPPORT_ITANIUMMANGLINGCANONICALIZER_H
 
-#include "llvm/ADT/StringRef.h"
-
 #include <cstddef>
 
 namespace llvm {
+
+class StringRef;
+
 /// Canonicalizer for mangled names.
 ///
 /// This class allows specifying a list of "equivalent" manglings. For example,
diff --git a/llvm/lib/Support/ItaniumManglingCanonicalizer.cpp b/llvm/lib/Support/ItaniumManglingCanonicalizer.cpp
index 7594c74b83b2e..9d3cf61459dd8 100644
--- a/llvm/lib/Support/ItaniumManglingCanonicalizer.cpp
+++ b/llvm/lib/Support/ItaniumManglingCanonicalizer.cpp
@@ -7,16 +7,12 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/ItaniumManglingCanonicalizer.h"
-
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Demangle/ItaniumDemangle.h"
 #include "llvm/Support/Allocator.h"
 
-#include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/FoldingSet.h"
-#include "llvm/ADT/StringRef.h"
-
 using namespace llvm;
 using llvm::itanium_demangle::ForwardTemplateReference;
 using llvm::itanium_demangle::Node;