diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -386,6 +386,13 @@
   on overload resolution, when the actual reason for the failure is loss of other qualifiers.
 - Clang's notes about unconvertible types in overload resolution failure now covers
   the source range of parameter declaration of the candidate function declaration.
+- Added a new diagnostic warning group
+  ``-Wdeprecated-redundant-constexpr-static-def``, under the existing
+  ``-Wdeprecated`` group. This controls warnings about out-of-line definitions
+  of 'static constexpr' data members that are unnecessary from C++17 onwards.
+
+ Bug Fixes in This Version
+ -------------------------
 
   *Example Code*:
 
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
@@ -186,6 +186,7 @@
 // For compatibility with GCC.
 def : DiagGroup<"deprecated-copy-dtor", [DeprecatedCopyWithDtor]>;
 def DeprecatedDeclarations : DiagGroup<"deprecated-declarations">;
+def DeprecatedRedundantConstexprStaticDef : DiagGroup<"deprecated-redundant-constexpr-static-def">;
 def UnavailableDeclarations : DiagGroup<"unavailable-declarations">;
 def UnguardedAvailabilityNew : DiagGroup<"unguarded-availability-new">;
 def UnguardedAvailability : DiagGroup<"unguarded-availability",
@@ -224,7 +225,9 @@
                                           DeprecatedThisCapture,
                                           DeprecatedType,
                                           DeprecatedVolatile,
-                                          DeprecatedWritableStr]>,
+                                          DeprecatedWritableStr,
+                                          DeprecatedRedundantConstexprStaticDef,
+                                          ]>,
                  DiagCategory<"Deprecations">;
 
 def CXX20Designator : DiagGroup<"c++20-designator">;
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
@@ -447,7 +447,7 @@
 def warn_deprecated_redundant_constexpr_static_def : Warning<
   "out-of-line definition of constexpr static data member is redundant "
   "in C++17 and is deprecated">,
-  InGroup<Deprecated>, DefaultIgnore;
+  InGroup<DeprecatedRedundantConstexprStaticDef>, DefaultIgnore;
 
 def warn_decl_shadow :
   Warning<"declaration shadows a %select{"
diff --git a/clang/test/SemaCXX/redundant-out-of-line-static-constexpr-member-def-diag.cpp b/clang/test/SemaCXX/redundant-out-of-line-static-constexpr-member-def-diag.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaCXX/redundant-out-of-line-static-constexpr-member-def-diag.cpp
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -std=c++17 -verify %s -Werror -Wdeprecated -Wno-error=deprecated-redundant-constexpr-static-def
+
+namespace {
+  struct A {
+    static constexpr int n = 0;
+    static constexpr int m = 0;
+  };
+  constexpr int A::n; // expected-warning{{out-of-line definition of constexpr static data member is redundant in C++17 and is deprecated}}
+  const int A::m; // expected-warning{{out-of-line definition of constexpr static data member is redundant in C++17 and is deprecated}}
+}