diff --git a/clang/docs/ClangCommandLineReference.rst b/clang/docs/ClangCommandLineReference.rst
--- a/clang/docs/ClangCommandLineReference.rst
+++ b/clang/docs/ClangCommandLineReference.rst
@@ -1367,6 +1367,10 @@
 
 .. option:: -Wdeprecated, -Wno-deprecated
 
+Within the given flag region, prevent warning about unknown warning enable/disable flags.
+
+.. option:: -Wstart-no-unknown-warning-option, -Wend-no-unknown-warning-option
+
 Enable warnings for deprecated constructs and define \_\_DEPRECATED
 
 .. option:: -Wframe-larger-than=<arg>, -Wframe-larger-than
diff --git a/clang/lib/Basic/Warnings.cpp b/clang/lib/Basic/Warnings.cpp
--- a/clang/lib/Basic/Warnings.cpp
+++ b/clang/lib/Basic/Warnings.cpp
@@ -189,6 +189,20 @@
         continue;
       }
 
+      if (Opt == "start-no-unknown-warning-option" ||
+          Opt == "end-no-unknown-warning-option") {
+        // These flags should explicitly take effect during the report phase,
+        // not the set-diagnostic phase, since they guard the processing of
+        // specific arguments.
+        if (Report) {
+          Diags.setSeverityForGroup(Flavor, "unknown-warning-option",
+                                    Opt == "start-no-unknown-warning-option"
+                                        ? diag::Severity::Ignored
+                                        : diag::Severity::Warning);
+        }
+        continue;
+      }
+
       if (Report) {
         if (DiagIDs->getDiagnosticsInGroup(Flavor, Opt, _Diags))
           EmitUnknownDiagWarning(Diags, Flavor, isPositive ? "-W" : "-Wno-",
diff --git a/clang/test/Frontend/warning-options.cpp b/clang/test/Frontend/warning-options.cpp
--- a/clang/test/Frontend/warning-options.cpp
+++ b/clang/test/Frontend/warning-options.cpp
@@ -1,8 +1,11 @@
 // RUN: %clang_cc1 -Wmonkey -Wno-monkey -Wno-unused-command-line-arguments \
-// RUN:        -Wno-unused-command-line-argument -Wmodule-build -Werror-vla -Rmodule-built %s 2>&1 | FileCheck %s
+// RUN:        -Wno-unused-command-line-argument -Wmodule-build -Werror-vla -Rmodule-built \
+// RUN:        -Wstart-no-unknown-warning-option -Wfoobarbaz -Wend-no-unknown-warning-option -Wplughxyzzy \
+// RUN:    %s 2>&1 | FileCheck %s
 // CHECK: unknown warning option '-Wmonkey'
 // CHECK: unknown warning option '-Wno-monkey'
 // CHECK: unknown warning option '-Wno-unused-command-line-arguments'; did you mean '-Wno-unused-command-line-argument'?
 // CHECK: unknown warning option '-Wmodule-build'; did you mean '-Wmodule-conflict'?
 // CHECK-NEXT: unknown -Werror warning specifier: '-Werror-vla'
+// CHECK: unknown warning option '-Wplughxyzzy'
 // CHECK: unknown remark option '-Rmodule-built'; did you mean '-Rmodule-build'?