Index: include/clang/Basic/DiagnosticGroups.td
===================================================================
--- include/clang/Basic/DiagnosticGroups.td
+++ include/clang/Basic/DiagnosticGroups.td
@@ -217,6 +217,7 @@
 def IncompleteModule : DiagGroup<"incomplete-module",
     [IncompleteUmbrella, NonModularIncludeInModule]>;
 
+def CXX11InlineNamespace : DiagGroup<"c++11-inline-namespace">;
 def InvalidNoreturn : DiagGroup<"invalid-noreturn">;
 def InvalidSourceEncoding : DiagGroup<"invalid-source-encoding">;
 def KNRPromotedParameter : DiagGroup<"knr-promoted-parameter">;
@@ -679,7 +680,8 @@
 
 // A warning group for warnings about using C++11 features as extensions in
 // earlier C++ versions.
-def CXX11 : DiagGroup<"c++11-extensions", [CXX11ExtraSemi, CXX11LongLong]>;
+def CXX11 : DiagGroup<"c++11-extensions", [CXX11ExtraSemi, CXX11InlineNamespace,
+                                           CXX11LongLong]>;
 
 // A warning group for warnings about using C++14 features as extensions in
 // earlier C++ versions.
Index: include/clang/Basic/DiagnosticParseKinds.td
===================================================================
--- include/clang/Basic/DiagnosticParseKinds.td
+++ include/clang/Basic/DiagnosticParseKinds.td
@@ -271,7 +271,7 @@
   "reference qualifiers on functions are incompatible with C++98">,
   InGroup<CXX98Compat>, DefaultIgnore;
 def ext_inline_namespace : ExtWarn<
-  "inline namespaces are a C++11 feature">, InGroup<CXX11>;
+  "inline namespaces are a C++11 feature">, InGroup<CXX11InlineNamespace>;
 def warn_cxx98_compat_inline_namespace : Warning<
   "inline namespaces are incompatible with C++98">,
   InGroup<CXX98Compat>, DefaultIgnore;