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
@@ -1414,7 +1414,8 @@
   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/Misc/warning-flags.c b/clang/test/Misc/warning-flags.c
--- a/clang/test/Misc/warning-flags.c
+++ b/clang/test/Misc/warning-flags.c
@@ -18,7 +18,7 @@
 
 The list of warnings below should NEVER grow.  It should gradually shrink to 0.
 
-CHECK: Warnings without flags (69):
+CHECK: Warnings without flags (68):
 
 CHECK-NEXT:   ext_expected_semi_decl_list
 CHECK-NEXT:   ext_explicit_specialization_storage_class
@@ -58,7 +58,6 @@
 CHECK-NEXT:   warn_ignoring_ftabstop_value
 CHECK-NEXT:   warn_implements_nscopying
 CHECK-NEXT:   warn_incompatible_qualified_id
-CHECK-NEXT:   warn_inline_namespace_reopened_noninline
 CHECK-NEXT:   warn_invalid_asm_cast_lvalue
 CHECK-NEXT:   warn_maynot_respond
 CHECK-NEXT:   warn_method_param_redefinition
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 +1,13 @@
+// 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 {
+  #ifndef SILENCE
+    inline namespace {} // expected-note {{previous definition}}
+    namespace {} // expected-warning {{inline namespace reopened as a non-inline namespace}}
+  #else
+    // expected-no-diagnostics
+    inline namespace {}
+    namespace {}
+  #endif
+}