Index: clang-tidy/modernize/RawStringLiteralCheck.h
===================================================================
--- clang-tidy/modernize/RawStringLiteralCheck.h
+++ clang-tidy/modernize/RawStringLiteralCheck.h
@@ -32,7 +32,7 @@
 private:
   void replaceWithRawStringLiteral(
       const ast_matchers::MatchFinder::MatchResult &Result,
-      const StringLiteral *Literal);
+      const StringLiteral *Literal, StringRef Replacement);
 
   std::string DelimiterStem;
 };
Index: clang-tidy/modernize/RawStringLiteralCheck.cpp
===================================================================
--- clang-tidy/modernize/RawStringLiteralCheck.cpp
+++ clang-tidy/modernize/RawStringLiteralCheck.cpp
@@ -121,19 +121,24 @@
   if (Literal->getLocStart().isMacroID())
     return;
 
-  if (containsEscapedCharacters(Result, Literal))
-    replaceWithRawStringLiteral(Result, Literal);
+  if (containsEscapedCharacters(Result, Literal)) {
+    std::string Replacement = asRawStringLiteral(Literal, DelimiterStem);
+    if (Replacement.length() <=
+        Lexer::MeasureTokenLength(Literal->getLocStart(), *Result.SourceManager,
+                                  getLangOpts()))
+      replaceWithRawStringLiteral(Result, Literal, Replacement);
+  }
 }
 
 void RawStringLiteralCheck::replaceWithRawStringLiteral(
-    const MatchFinder::MatchResult &Result, const StringLiteral *Literal) {
+    const MatchFinder::MatchResult &Result, const StringLiteral *Literal,
+    StringRef Replacement) {
   CharSourceRange CharRange = Lexer::makeFileCharRange(
       CharSourceRange::getTokenRange(Literal->getSourceRange()),
       *Result.SourceManager, getLangOpts());
   diag(Literal->getLocStart(),
        "escaped string literal can be written as a raw string literal")
-      << FixItHint::CreateReplacement(
-             CharRange, asRawStringLiteral(Literal, DelimiterStem));
+      << FixItHint::CreateReplacement(CharRange, Replacement);
 }
 
 } // namespace modernize
Index: test/clang-tidy/modernize-raw-string-literal.cpp
===================================================================
--- test/clang-tidy/modernize-raw-string-literal.cpp
+++ test/clang-tidy/modernize-raw-string-literal.cpp
@@ -55,6 +55,10 @@
 wchar_t const *const WideLiteral(L"foobie\\bletch");
 wchar_t const *const WideRawLiteral(LR"(foobie\\bletch)");
 
+// Don't replace these, because the raw literal would be longer.
+char const *const JustAQuote("quote:\'");
+char const *const NeedDelimiter("\":)\"");
+
 char const *const SingleQuote("goink\'frob");
 // CHECK-MESSAGES: :[[@LINE-1]]:31: warning: {{.*}} can be written as a raw string literal
 // CHECK-XFIXES: {{^}}char const *const SingleQuote(R"(goink'frob)");{{$}}