diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -382,6 +382,8 @@
 def PrivateModule : DiagGroup<"private-module">;
 
 def CXX11InlineNamespace : DiagGroup<"c++11-inline-namespace">;
+def InlineNamespaceReopenedNoninline
+    : DiagGroup<"inline-namespace-reopened-noninline">;
 def InvalidNoreturn : DiagGroup<"invalid-noreturn">;
 def InvalidSourceEncoding : DiagGroup<"invalid-source-encoding">;
 def KNRPromotedParameter : DiagGroup<"knr-promoted-parameter">;
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1411,7 +1411,8 @@
   DefaultIgnore, InGroup<CXXPre17Compat>;
 
 def warn_inline_namespace_reopened_noninline : Warning<
-  "inline namespace reopened as a non-inline namespace">;
+  "inline namespace reopened as a non-inline namespace">,
+  InGroup<InlineNamespaceReopenedNoninline>;
 def err_inline_namespace_mismatch : Error<
   "non-inline namespace cannot be reopened as inline">;
 
diff --git a/clang/test/SemaCXX/warn-inline-namespace-reopened-noninline-disable.cpp b/clang/test/SemaCXX/warn-inline-namespace-reopened-noninline-disable.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaCXX/warn-inline-namespace-reopened-noninline-disable.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -fsyntax-only -Wall -verify -std=c++11 %s
+// RUN: %clang_cc1 -fsyntax-only -Wall -Wno-inline-namespace-reopened-noninline -DSILENCE -verify -std=c++11 %s
+
+namespace X {
+  inline namespace {}
+  #ifndef SILENCE
+    namespace {} // expected-warning {{inline namespace reopened as a non-inline namespace}}
+  #else
+    namespace {} // expected-no-diagnostics
+  #endif
+}