Index: cfe/trunk/lib/Format/Format.cpp
===================================================================
--- cfe/trunk/lib/Format/Format.cpp
+++ cfe/trunk/lib/Format/Format.cpp
@@ -1652,7 +1652,7 @@
       for (FormatToken *FormatTok = Line->First; FormatTok;
            FormatTok = FormatTok->Next) {
         StringRef Input = FormatTok->TokenText;
-        if (!FormatTok->isStringLiteral() ||
+        if (FormatTok->Finalized || !FormatTok->isStringLiteral() ||
             // NB: testing for not starting with a double quote to avoid
             // breaking
             // `template strings`.
Index: cfe/trunk/unittests/Format/FormatTestJS.cpp
===================================================================
--- cfe/trunk/unittests/Format/FormatTestJS.cpp
+++ cfe/trunk/unittests/Format/FormatTestJS.cpp
@@ -1236,6 +1236,14 @@
   // Code below fits into 15 chars *after* removing the \ escape.
   verifyFormat("var x = 'fo\"o';", "var x = \"fo\\\"o\";",
                getGoogleJSStyleWithColumns(15));
+  verifyFormat("// clang-format off\n"
+               "let x = \"double\";\n"
+               "// clang-format on\n"
+               "let x = 'single';\n",
+               "// clang-format off\n"
+               "let x = \"double\";\n"
+               "// clang-format on\n"
+               "let x = \"single\";\n");
 }
 
 TEST_F(FormatTestJS, RequoteStringsDouble) {