Index: clang/docs/ClangFormatStyleOptions.rst
===================================================================
--- clang/docs/ClangFormatStyleOptions.rst
+++ clang/docs/ClangFormatStyleOptions.rst
@@ -948,7 +948,7 @@
         int x;
       }
 
-  * ``bool AfterExternBlock`` Wrap extern blocks.
+  * ``bool AfterExternBlock`` Wrap extern blocks; Partially superseded by IndentExternBlock
 
     .. code-block:: c++
 
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -256,6 +256,23 @@
 ------------
 
 
+- Option ``IndentExternBlock`` has been added to optionally apply indenting inside ``extern "C"`` and ``extern "C++"`` blocks.
+
+- ``IndentExternBlock`` option accepts ``AfterExternBlock`` to use the old behavior, as well as Indent and NoIndent options, which map to true and false, respectively.
+
+  .. code-block:: c++
+
+    Indent:                       NoIndent:
+      #ifdef __cplusplus          extern "C++" {
+      extern "C" {
+      #endif
+  
+          void f(void);           void f(void);
+  
+      #ifdef __cplusplus
+      }                           }
+      #endif
+
 - Option ``IndentCaseBlocks`` has been added to support treating the block
   following a switch case label as a scope block which gets indented itself.
   It helps avoid having the closing bracket align with the switch statement's
Index: clang/include/clang/Format/Format.h
===================================================================
--- clang/include/clang/Format/Format.h
+++ clang/include/clang/Format/Format.h
@@ -1004,7 +1004,7 @@
     ///   }
     /// \endcode
     bool AfterUnion;
-    /// Wrap extern blocks.
+    /// Wrap extern blocks; Partially superseded by IndentExternBlock
     /// \code
     ///   true:
     ///   extern "C"
@@ -1518,6 +1518,41 @@
   /// \endcode
   bool IndentWrappedFunctionNames;
 
+  /// Indents extern blocks
+  enum IndentExternBlockStyle {
+    /// Does not indent extern blocks.
+    /// \code
+    ///  extern "C" {
+    ///  void foo();
+    ///  }
+    /// \endcode
+    IEBS_NoIndent,
+    /// Indents extern blocks.
+    /// \code
+    ///  extern "C" {
+    ///    void foo();
+    ///  }
+    /// \endcode
+    IEBS_Indent,
+    /// Backwards compatible with AfterExternBlock's indenting.
+    /// AfterExternBlock: true
+    /// \code
+    /// extern "C"
+    /// {
+    ///   void foo();
+    /// }
+    /// \endcode
+    /// AfterExternBlock: false
+    /// \code
+    /// extern "C" {
+    /// void foo();
+    /// }
+    /// \endcode
+    IEBS_AfterExternBlock,
+  };
+    
+  IndentExternBlockStyle IndentExternBlock;
+
   /// A vector of prefixes ordered by the desired groups for Java imports.
   ///
   /// Each group is separated by a newline. Static imports will also follow the
@@ -2278,6 +2313,7 @@
            IndentPPDirectives == R.IndentPPDirectives &&
            IndentWidth == R.IndentWidth && Language == R.Language &&
            IndentWrappedFunctionNames == R.IndentWrappedFunctionNames &&
+           IndentExternBlock == R.IndentExternBlock &&
            JavaImportGroups == R.JavaImportGroups &&
            JavaScriptQuotes == R.JavaScriptQuotes &&
            JavaScriptWrapImports == R.JavaScriptWrapImports &&
Index: clang/lib/Format/Format.cpp
===================================================================
--- clang/lib/Format/Format.cpp
+++ clang/lib/Format/Format.cpp
@@ -204,6 +204,18 @@
     IO.enumCase(Value, "true", FormatStyle::BWACS_Always);
   }
 };
+  
+template <>
+struct ScalarEnumerationTraits<FormatStyle::IndentExternBlockStyle> {
+  static void
+  enumeration(IO &IO, FormatStyle::IndentExternBlockStyle &Value) {
+    IO.enumCase(Value, "AfterExternBlock", FormatStyle::IEBS_AfterExternBlock);
+    IO.enumCase(Value, "Indent", FormatStyle::IEBS_Indent);
+    IO.enumCase(Value, "NoIndent", FormatStyle::IEBS_NoIndent);
+    IO.enumCase(Value, "true", FormatStyle::IEBS_Indent);
+    IO.enumCase(Value, "false", FormatStyle::IEBS_NoIndent);
+  }
+};
 
 template <>
 struct ScalarEnumerationTraits<FormatStyle::BreakConstructorInitializersStyle> {
@@ -513,6 +525,7 @@
     IO.mapOptional("IndentWidth", Style.IndentWidth);
     IO.mapOptional("IndentWrappedFunctionNames",
                    Style.IndentWrappedFunctionNames);
+    IO.mapOptional("IndentExternBlock", Style.IndentExternBlock);
     IO.mapOptional("InsertTrailingCommas", Style.InsertTrailingCommas);
     IO.mapOptional("JavaImportGroups", Style.JavaImportGroups);
     IO.mapOptional("JavaScriptQuotes", Style.JavaScriptQuotes);
Index: clang/lib/Format/UnwrappedLineParser.cpp
===================================================================
--- clang/lib/Format/UnwrappedLineParser.cpp
+++ clang/lib/Format/UnwrappedLineParser.cpp
@@ -1115,9 +1115,9 @@
       if (FormatTok->Tok.is(tok::l_brace)) {
         if (Style.BraceWrapping.AfterExternBlock) {
           addUnwrappedLine();
-          parseBlock(/*MustBeDeclaration=*/true);
+          parseBlock(/*MustBeDeclaration=*/true, /*AddLevel=*/Style.BraceWrapping.AfterExternBlock);
         } else {
-          parseBlock(/*MustBeDeclaration=*/true, /*AddLevel=*/false);
+          parseBlock(/*MustBeDeclaration=*/true, /*AddLevel=*/Style.IndentExternBlock == FormatStyle::IEBS_Indent);
         }
         addUnwrappedLine();
         return;
Index: clang/unittests/Format/FormatTest.cpp
===================================================================
--- clang/unittests/Format/FormatTest.cpp
+++ clang/unittests/Format/FormatTest.cpp
@@ -2538,6 +2538,39 @@
                "}",
                Style);
 }
+  
+TEST_F(FormatTest, IndentExternBlockStyle) {
+  FormatStyle Style = getLLVMStyle();
+  Style.IndentWidth = 2;
+  
+  Style.IndentExternBlock = FormatStyle::IEBS_Indent;
+  verifyFormat("extern \"C\" { /*9*/\n}", Style);
+  verifyFormat("extern \"C\" {\n"
+               "  int foo10();\n"
+               "}", Style);
+  
+  Style.IndentExternBlock = FormatStyle::IEBS_NoIndent;
+  verifyFormat("extern \"C\" { /*11*/\n}", Style);
+  verifyFormat("extern \"C\" {\n"
+               "int foo12();\n"
+               "}", Style);
+  
+  Style.BreakBeforeBraces = FormatStyle::BS_Custom;
+  
+  Style.BraceWrapping.AfterExternBlock = true;
+  Style.IndentExternBlock = FormatStyle::IEBS_AfterExternBlock;
+  verifyFormat("extern \"C\"\n{ /*13*/\n}", Style);
+  verifyFormat("extern \"C\"\n{\n"
+               "  int foo14();\n"
+               "}", Style);
+  
+  Style.BraceWrapping.AfterExternBlock = false;
+  Style.IndentExternBlock = FormatStyle::IEBS_AfterExternBlock;
+  verifyFormat("extern \"C\" { /*15*/\n}", Style);
+  verifyFormat("extern \"C\" {\n"
+               "int foo16();\n"
+               "}", Style);
+}
 
 TEST_F(FormatTest, FormatsInlineASM) {
   verifyFormat("asm(\"xyz\" : \"=a\"(a), \"=d\"(b) : \"a\"(data));");
@@ -13715,6 +13748,13 @@
   CHECK_PARSE("AllowShortIfStatementsOnASingleLine: true",
               AllowShortIfStatementsOnASingleLine,
               FormatStyle::SIS_WithoutElse);
+  
+  Style.IndentExternBlock = FormatStyle::IEBS_Indent;
+  CHECK_PARSE("IndentExternBlock: AfterExternBlock", IndentExternBlock, FormatStyle::IEBS_AfterExternBlock);
+  CHECK_PARSE("IndentExternBlock: Indent", IndentExternBlock, FormatStyle::IEBS_Indent);
+  CHECK_PARSE("IndentExternBlock: NoIndent", IndentExternBlock, FormatStyle::IEBS_NoIndent);
+  CHECK_PARSE("IndentExternBlock: true", IndentExternBlock, FormatStyle::IEBS_Indent);
+  CHECK_PARSE("IndentExternBlock: false", IndentExternBlock, FormatStyle::IEBS_NoIndent);
 
   // FIXME: This is required because parsing a configuration simply overwrites
   // the first N elements of the list instead of resetting it.