diff --git a/libcxxabi/src/demangle/cp-to-llvm.sh b/libcxxabi/src/demangle/cp-to-llvm.sh
--- a/libcxxabi/src/demangle/cp-to-llvm.sh
+++ b/libcxxabi/src/demangle/cp-to-llvm.sh
@@ -5,7 +5,8 @@
 
 set -e
 
-FILES="ItaniumDemangle.h StringView.h Utility.h README.txt"
+cd $(dirname $0)
+HDRS="ItaniumDemangle.h StringView.h Utility.h"
 LLVM_DEMANGLE_DIR=$1
 
 if [[ -z "$LLVM_DEMANGLE_DIR" ]]; then
@@ -21,7 +22,14 @@
 echo
 
 if [[ $ANSWER =~ ^[Yy]$ ]]; then
-    for I in $FILES ; do
-        cp $I $LLVM_DEMANGLE_DIR/$I
+    cp -f README.txt $LLVM_DEMANGLE_DIR
+    chmod -w $LLVM_DEMANGLE_DIR/README.txt
+    for I in $HDRS ; do
+	rm -f $LLVM_DEMANGLE_DIR/$I
+	cat - $I >$LLVM_DEMANGLE_DIR/$I <<EOF
+// Do not edit! -*- read-only -*-
+// See README.txt for instructions
+EOF
+	chmod -w $LLVM_DEMANGLE_DIR/$I
     done
 fi
diff --git a/llvm/include/llvm/Demangle/ItaniumDemangle.h b/llvm/include/llvm/Demangle/ItaniumDemangle.h
--- a/llvm/include/llvm/Demangle/ItaniumDemangle.h
+++ b/llvm/include/llvm/Demangle/ItaniumDemangle.h
@@ -1,3 +1,5 @@
+// Do not edit! -*- read-only -*-
+// See README.txt for instructions
 //===------------------------- ItaniumDemangle.h ----------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
@@ -11,8 +13,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_DEMANGLE_ITANIUMDEMANGLE_H
-#define LLVM_DEMANGLE_ITANIUMDEMANGLE_H
+#ifndef DEMANGLE_ITANIUMDEMANGLE_H
+#define DEMANGLE_ITANIUMDEMANGLE_H
 
 // FIXME: (possibly) incomplete list of features that clang mangles that this
 // file does not yet support:
@@ -5749,4 +5751,4 @@
 
 DEMANGLE_NAMESPACE_END
 
-#endif // LLVM_DEMANGLE_ITANIUMDEMANGLE_H
+#endif // DEMANGLE_ITANIUMDEMANGLE_H
diff --git a/llvm/include/llvm/Demangle/StringView.h b/llvm/include/llvm/Demangle/StringView.h
--- a/llvm/include/llvm/Demangle/StringView.h
+++ b/llvm/include/llvm/Demangle/StringView.h
@@ -1,3 +1,5 @@
+// Do not edit! -*- read-only -*-
+// See README.txt for instructions
 //===--- StringView.h -------------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
@@ -10,8 +12,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_DEMANGLE_STRINGVIEW_H
-#define LLVM_DEMANGLE_STRINGVIEW_H
+#ifndef DEMANGLE_STRINGVIEW_H
+#define DEMANGLE_STRINGVIEW_H
 
 #include "DemangleConfig.h"
 #include <cassert>
diff --git a/llvm/include/llvm/Demangle/Utility.h b/llvm/include/llvm/Demangle/Utility.h
--- a/llvm/include/llvm/Demangle/Utility.h
+++ b/llvm/include/llvm/Demangle/Utility.h
@@ -1,3 +1,5 @@
+// Do not edit! -*- read-only -*-
+// See README.txt for instructions
 //===--- Utility.h ----------------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
@@ -10,8 +12,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_DEMANGLE_UTILITY_H
-#define LLVM_DEMANGLE_UTILITY_H
+#ifndef DEMANGLE_UTILITY_H
+#define DEMANGLE_UTILITY_H
 
 #include "StringView.h"
 #include <array>