diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index f96cebbde3d82..e98c0cde2e6b3 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -43,6 +43,10 @@ code bases.
 C/C++ Language Potentially Breaking Changes
 -------------------------------------------
 
+- Clang now supports raw string literals in ``-std=gnuXY`` mode as an extension in
+  C99 and later. This behaviour can also be overridden using ``-f[no-]raw-string-literals``.
+  Support of raw string literals in C++ is not affected. Fixes (#GH85703).
+
 C++ Specific Potentially Breaking Changes
 -----------------------------------------
 - Clang now diagnoses function/variable templates that shadow their own template parameters, e.g. ``template<class T> void T();``.
diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
index ed3fd9b1c4a55..6185dd4691d8a 100644
--- a/clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ b/clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -375,6 +375,8 @@ def err_drv_negative_columns : Error<
   "invalid value '%1' in '%0', value must be 'none' or a positive integer">;
 def err_drv_small_columns : Error<
   "invalid value '%1' in '%0', value must be '%2' or greater">;
+def warn_drv_fraw_string_literals_in_cxx : Warning<
+  "ignoring '-f%select{no-|}0raw-string-literals', which is only valid for C">;
 
 def err_drv_invalid_malign_branch_EQ : Error<
   "invalid argument '%0' to -malign-branch=; each element must be one of: %1">;
diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
index 8ef6700ecdc78..96bd339bb1851 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -454,6 +454,8 @@ LANGOPT(MatrixTypes, 1, 0, "Enable or disable the builtin matrix type")
 
 LANGOPT(CXXAssumptions, 1, 1, "Enable or disable codegen and compile-time checks for C++23's [[assume]] attribute")
 
+LANGOPT(RawStringLiterals, 1, 0, "Enable or disable raw string literals")
+
 ENUM_LANGOPT(StrictFlexArraysLevel, StrictFlexArraysLevelKind, 2,
              StrictFlexArraysLevelKind::Default,
              "Rely on strict definition of flexible arrays")
diff --git a/clang/include/clang/Basic/LangStandard.h b/clang/include/clang/Basic/LangStandard.h
index 8e25afc833661..49594a49e9f37 100644
--- a/clang/include/clang/Basic/LangStandard.h
+++ b/clang/include/clang/Basic/LangStandard.h
@@ -130,6 +130,13 @@ struct LangStandard {
   /// hasDigraphs - Language supports digraphs.
   bool hasDigraphs() const { return Flags & Digraphs; }
 
+  /// hasRawStringLiterals - Language supports R"()" raw string literals.
+  bool hasRawStringLiterals() const {
+    // GCC supports raw string literals in C99 and later, but not in C++
+    // before C++11.
+    return isCPlusPlus11() || (!isCPlusPlus() && isC99() && isGNUMode());
+  }
+
   /// isGNUMode - Language includes GNU extensions.
   bool isGNUMode() const { return Flags & GNUMode; }
 
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index f745e573eb268..32e6c10e1251b 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -4142,6 +4142,12 @@ def fenable_matrix : Flag<["-"], "fenable-matrix">, Group<f_Group>,
     HelpText<"Enable matrix data type and related builtin functions">,
     MarshallingInfoFlag<LangOpts<"MatrixTypes">>;
 
+defm raw_string_literals : BoolFOption<"raw-string-literals",
+    LangOpts<"RawStringLiterals">, Default<std#".hasRawStringLiterals()">,
+    PosFlag<SetTrue, [], [], "Enable">,
+    NegFlag<SetFalse, [], [], "Disable">,
+    BothFlags<[], [ClangOption, CC1Option], " raw string literals">>;
+
 def fzero_call_used_regs_EQ
     : Joined<["-"], "fzero-call-used-regs=">, Group<f_Group>,
     Visibility<[ClangOption, CC1Option]>,
diff --git a/clang/lib/Basic/LangOptions.cpp b/clang/lib/Basic/LangOptions.cpp
index a0adfbf61840e..c34f0ed5ed717 100644
--- a/clang/lib/Basic/LangOptions.cpp
+++ b/clang/lib/Basic/LangOptions.cpp
@@ -124,6 +124,7 @@ void LangOptions::setLangDefaults(LangOptions &Opts, Language Lang,
   Opts.HexFloats = Std.hasHexFloats();
   Opts.WChar = Std.isCPlusPlus();
   Opts.Digraphs = Std.hasDigraphs();
+  Opts.RawStringLiterals = Std.hasRawStringLiterals();
 
   Opts.HLSL = Lang == Language::HLSL;
   if (Opts.HLSL && Opts.IncludeDefaultHeader)
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 766a9b91e3c0a..c99bfe4efc413 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -6536,6 +6536,8 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   Args.AddLastArg(CmdArgs, options::OPT_fheinous_gnu_extensions);
   Args.AddLastArg(CmdArgs, options::OPT_fdigraphs, options::OPT_fno_digraphs);
   Args.AddLastArg(CmdArgs, options::OPT_fzero_call_used_regs_EQ);
+  Args.AddLastArg(CmdArgs, options::OPT_fraw_string_literals,
+                  options::OPT_fno_raw_string_literals);
 
   if (Args.hasFlag(options::OPT_femulated_tls, options::OPT_fno_emulated_tls,
                    Triple.hasDefaultEmulatedTLS()))
diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index 89e6c19b0af45..71865bb061f57 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -3850,6 +3850,7 @@ LangOptions getFormattingLangOpts(const FormatStyle &Style) {
   // the sequence "<::" will be unconditionally treated as "[:".
   // Cf. Lexer::LexTokenInternal.
   LangOpts.Digraphs = LexingStd >= FormatStyle::LS_Cpp11;
+  LangOpts.RawStringLiterals = LexingStd >= FormatStyle::LS_Cpp11;
 
   LangOpts.LineComment = 1;
   bool AlternativeOperators = Style.isCpp();
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 1f1f5440ddd75..963f1d1bc34f5 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -610,6 +610,15 @@ static bool FixupInvocation(CompilerInvocation &Invocation,
     LangOpts.NewAlignOverride = 0;
   }
 
+  // The -f[no-]raw-string-literals option is only valid in C.
+  if ((Args.hasArg(OPT_fraw_string_literals) ||
+       Args.hasArg(OPT_fno_raw_string_literals)) &&
+      LangOpts.CPlusPlus) {
+    Diags.Report(diag::warn_drv_fraw_string_literals_in_cxx)
+        << bool(LangOpts.RawStringLiterals);
+    LangOpts.RawStringLiterals = LangOpts.CPlusPlus11;
+  }
+
   // Prevent the user from specifying both -fsycl-is-device and -fsycl-is-host.
   if (LangOpts.SYCLIsDevice && LangOpts.SYCLIsHost)
     Diags.Report(diag::err_drv_argument_not_allowed_with) << "-fsycl-is-device"
diff --git a/clang/lib/Lex/Lexer.cpp b/clang/lib/Lex/Lexer.cpp
index c98645993abe0..67d75c1140b23 100644
--- a/clang/lib/Lex/Lexer.cpp
+++ b/clang/lib/Lex/Lexer.cpp
@@ -3867,7 +3867,7 @@ bool Lexer::LexTokenInternal(Token &Result, bool TokAtPhysicalStartOfLine) {
                                tok::utf16_char_constant);
 
       // UTF-16 raw string literal
-      if (Char == 'R' && LangOpts.CPlusPlus11 &&
+      if (Char == 'R' && LangOpts.RawStringLiterals &&
           getCharAndSize(CurPtr + SizeTmp, SizeTmp2) == '"')
         return LexRawStringLiteral(Result,
                                ConsumeChar(ConsumeChar(CurPtr, SizeTmp, Result),
@@ -3889,7 +3889,7 @@ bool Lexer::LexTokenInternal(Token &Result, bool TokAtPhysicalStartOfLine) {
                                   SizeTmp2, Result),
               tok::utf8_char_constant);
 
-        if (Char2 == 'R' && LangOpts.CPlusPlus11) {
+        if (Char2 == 'R' && LangOpts.RawStringLiterals) {
           unsigned SizeTmp3;
           char Char3 = getCharAndSize(CurPtr + SizeTmp + SizeTmp2, SizeTmp3);
           // UTF-8 raw string literal
@@ -3925,7 +3925,7 @@ bool Lexer::LexTokenInternal(Token &Result, bool TokAtPhysicalStartOfLine) {
                                tok::utf32_char_constant);
 
       // UTF-32 raw string literal
-      if (Char == 'R' && LangOpts.CPlusPlus11 &&
+      if (Char == 'R' && LangOpts.RawStringLiterals &&
           getCharAndSize(CurPtr + SizeTmp, SizeTmp2) == '"')
         return LexRawStringLiteral(Result,
                                ConsumeChar(ConsumeChar(CurPtr, SizeTmp, Result),
@@ -3940,7 +3940,7 @@ bool Lexer::LexTokenInternal(Token &Result, bool TokAtPhysicalStartOfLine) {
     // Notify MIOpt that we read a non-whitespace/non-comment token.
     MIOpt.ReadToken();
 
-    if (LangOpts.CPlusPlus11) {
+    if (LangOpts.RawStringLiterals) {
       Char = getCharAndSize(CurPtr, SizeTmp);
 
       if (Char == '"')
@@ -3963,7 +3963,7 @@ bool Lexer::LexTokenInternal(Token &Result, bool TokAtPhysicalStartOfLine) {
                               tok::wide_string_literal);
 
     // Wide raw string literal.
-    if (LangOpts.CPlusPlus11 && Char == 'R' &&
+    if (LangOpts.RawStringLiterals && Char == 'R' &&
         getCharAndSize(CurPtr + SizeTmp, SizeTmp2) == '"')
       return LexRawStringLiteral(Result,
                                ConsumeChar(ConsumeChar(CurPtr, SizeTmp, Result),
diff --git a/clang/test/Driver/fraw-string-literals-cxx.cpp b/clang/test/Driver/fraw-string-literals-cxx.cpp
new file mode 100644
index 0000000000000..cb1133711a030
--- /dev/null
+++ b/clang/test/Driver/fraw-string-literals-cxx.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang -fraw-string-literals    -fsyntax-only -std=c++03   %s 2>&1 | FileCheck --check-prefix=CHECK-POS %s
+// RUN: %clang -fraw-string-literals    -fsyntax-only -std=gnu++03 %s 2>&1 | FileCheck --check-prefix=CHECK-POS %s
+// RUN: %clang -fno-raw-string-literals -fsyntax-only -std=c++03   %s 2>&1 | FileCheck --check-prefix=CHECK-NEG %s
+// RUN: %clang -fno-raw-string-literals -fsyntax-only -std=gnu++03 %s 2>&1 | FileCheck --check-prefix=CHECK-NEG %s
+// RUN: %clang -fraw-string-literals    -fsyntax-only -std=c++11   %s 2>&1 | FileCheck --check-prefix=CHECK-POS %s
+// RUN: %clang -fraw-string-literals    -fsyntax-only -std=gnu++11 %s 2>&1 | FileCheck --check-prefix=CHECK-POS %s
+// RUN: %clang -fno-raw-string-literals -fsyntax-only -std=c++11   %s 2>&1 | FileCheck --check-prefix=CHECK-NEG %s
+// RUN: %clang -fno-raw-string-literals -fsyntax-only -std=gnu++11 %s 2>&1 | FileCheck --check-prefix=CHECK-NEG %s
+
+// CHECK-POS: ignoring '-fraw-string-literals', which is only valid for C
+// CHECK-NEG: ignoring '-fno-raw-string-literals', which is only valid for C
diff --git a/clang/test/Lexer/raw-string-ext.c b/clang/test/Lexer/raw-string-ext.c
new file mode 100644
index 0000000000000..feac8d0c4beaf
--- /dev/null
+++ b/clang/test/Lexer/raw-string-ext.c
@@ -0,0 +1,39 @@
+// RUN: %clang_cc1 -fsyntax-only -std=gnu11 -verify=supported %s
+// RUN: %clang_cc1 -fsyntax-only -std=c11 -fraw-string-literals -verify=supported %s
+// RUN: %clang_cc1 -fsyntax-only -std=gnu89 -verify=unsupported %s
+// RUN: %clang_cc1 -fsyntax-only -std=c11 -verify=unsupported %s
+// RUN: %clang_cc1 -fsyntax-only -std=gnu11 -fno-raw-string-literals -verify=unsupported %s
+
+// RUN: %clang_cc1 -x c++ -fsyntax-only -Wno-unused -std=c++03 -verify=unsupported,cxx-unsupported %s
+// RUN: %clang_cc1 -x c++ -fsyntax-only -Wno-unused -std=gnu++03 -verify=unsupported,cxx-unsupported %s
+// RUN: %clang_cc1 -x c++ -fsyntax-only -Wno-unused -std=c++03 -fraw-string-literals -verify=unsupported,cxx-unsupported,yes %s
+// RUN: %clang_cc1 -x c++ -fsyntax-only -Wno-unused -std=gnu++03 -fraw-string-literals -verify=unsupported,cxx-unsupported,yes %s
+// RUN: %clang_cc1 -x c++ -fsyntax-only -Wno-unused -std=c++11 -verify=supported,cxx %s
+// RUN: %clang_cc1 -x c++ -fsyntax-only -Wno-unused -std=gnu++11 -verify=supported,cxx %s
+// RUN: %clang_cc1 -x c++ -fsyntax-only -Wno-unused -std=c++11 -fno-raw-string-literals -verify=supported,no %s
+// RUN: %clang_cc1 -x c++ -fsyntax-only -Wno-unused -std=gnu++11 -fno-raw-string-literals -verify=supported,no %s
+
+// GCC supports raw string literals in C99 and later in '-std=gnuXY' mode; we
+// additionally provide '-f[no-]raw-string-literals' to enable/disable them
+// explicitly in C.
+//
+// We do not allow disabling or enabling raw string literals in C++ mode if
+// they’re not already enabled by the language standard.
+
+// Driver warnings.
+// yes-warning@* {{ignoring '-fraw-string-literals', which is only valid for C}}
+// no-warning@* {{ignoring '-fno-raw-string-literals', which is only valid for C}}
+
+void f() {
+  (void) R"foo()foo"; // unsupported-error {{use of undeclared identifier 'R'}} cxx-unsupported-error {{expected ';' after expression}}
+  (void) LR"foo()foo"; // unsupported-error {{use of undeclared identifier 'LR'}} cxx-unsupported-error {{expected ';' after expression}}
+  (void) uR"foo()foo"; // unsupported-error {{use of undeclared identifier 'uR'}} cxx-unsupported-error {{expected ';' after expression}}
+  (void) u8R"foo()foo"; // unsupported-error {{use of undeclared identifier 'u8R'}} cxx-unsupported-error {{expected ';' after expression}}
+  (void) UR"foo()foo"; // unsupported-error {{use of undeclared identifier 'UR'}} cxx-unsupported-error {{expected ';' after expression}}
+}
+
+// supported-error@* {{missing terminating delimiter}}
+// supported-error@* {{expected expression}}
+// supported-error@* {{expected ';' after top level declarator}}
+#define R "bar"
+const char* s =  R"foo(";