diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -1279,17 +1279,18 @@
     if (FormatTok->Tok.is(tok::string_literal)) {
       nextToken();
       if (FormatTok->Tok.is(tok::l_brace)) {
-        if (!Style.IndentExternBlock) {
-          if (Style.BraceWrapping.AfterExternBlock) {
-            addUnwrappedLine();
-          }
-          unsigned AddLevels = Style.BraceWrapping.AfterExternBlock ? 1u : 0u;
-          parseBlock(/*MustBeDeclaration=*/true, AddLevels);
-        } else {
-          unsigned AddLevels =
-              Style.IndentExternBlock == FormatStyle::IEBS_Indent ? 1u : 0u;
-          parseBlock(/*MustBeDeclaration=*/true, AddLevels);
-        }
+        if (Style.BraceWrapping.AfterExternBlock)
+          addUnwrappedLine();
+        // Either we indent or for backwards compatibility we follow the
+        // AfterExternBlock style.
+        unsigned AddLevels =
+            (Style.IndentExternBlock == FormatStyle::IEBS_Indent) ||
+                    (Style.BraceWrapping.AfterExternBlock &&
+                     Style.IndentExternBlock ==
+                         FormatStyle::IEBS_AfterExternBlock)
+                ? 1u
+                : 0u;
+        parseBlock(/*MustBeDeclaration=*/true, AddLevels);
         addUnwrappedLine();
         return;
       }
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -3835,36 +3835,66 @@
   Style.IndentWidth = 2;
 
   Style.IndentExternBlock = FormatStyle::IEBS_Indent;
-  verifyFormat("extern \"C\" { /*9*/\n}", Style);
+  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\" { /*11*/\n"
+               "}",
+               Style);
   verifyFormat("extern \"C\" {\n"
                "int foo12();\n"
                "}",
                Style);
 
-  Style.IndentExternBlock = FormatStyle::IEBS_AfterExternBlock;
   Style.BreakBeforeBraces = FormatStyle::BS_Custom;
   Style.BraceWrapping.AfterExternBlock = true;
-  verifyFormat("extern \"C\"\n{ /*13*/\n}", Style);
+  Style.IndentExternBlock = FormatStyle::IEBS_Indent;
+  verifyFormat("extern \"C\"\n"
+               "{ /*13*/\n"
+               "}",
+               Style);
   verifyFormat("extern \"C\"\n{\n"
                "  int foo14();\n"
                "}",
                Style);
 
-  Style.IndentExternBlock = FormatStyle::IEBS_AfterExternBlock;
-  Style.BreakBeforeBraces = FormatStyle::BS_Custom;
   Style.BraceWrapping.AfterExternBlock = false;
-  verifyFormat("extern \"C\" { /*15*/\n}", Style);
+  Style.IndentExternBlock = FormatStyle::IEBS_NoIndent;
+  verifyFormat("extern \"C\" { /*15*/\n"
+               "}",
+               Style);
   verifyFormat("extern \"C\" {\n"
                "int foo16();\n"
                "}",
                Style);
+
+  Style.BraceWrapping.AfterExternBlock = true;
+  verifyFormat("extern \"C\"\n"
+               "{ /*13*/\n"
+               "}",
+               Style);
+  verifyFormat("extern \"C\"\n"
+               "{\n"
+               "int foo14();\n"
+               "}",
+               Style);
+
+  Style.IndentExternBlock = FormatStyle::IEBS_Indent;
+  verifyFormat("extern \"C\"\n"
+               "{ /*13*/\n"
+               "}",
+               Style);
+  verifyFormat("extern \"C\"\n"
+               "{\n"
+               "  int foo14();\n"
+               "}",
+               Style);
 }
 
 TEST_F(FormatTest, FormatsInlineASM) {