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
@@ -671,8 +671,11 @@
 def Switch         : DiagGroup<"switch">;
 def ImplicitFallthroughPerFunction :
   DiagGroup<"implicit-fallthrough-per-function">;
+def ImplicitFallthroughUnreachable :
+  DiagGroup<"implicit-fallthrough-unreachable">;
 def ImplicitFallthrough  : DiagGroup<"implicit-fallthrough",
-                                     [ImplicitFallthroughPerFunction]>;
+                                     [ImplicitFallthroughPerFunction,
+                                      ImplicitFallthroughUnreachable]>;
 def InvalidPPToken : DiagGroup<"invalid-pp-token">;
 def Trigraphs      : DiagGroup<"trigraphs">;
 
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
@@ -9580,7 +9580,7 @@
   "fallthrough annotation does not directly precede switch label">;
 def warn_fallthrough_attr_unreachable : Warning<
   "fallthrough annotation in unreachable code">,
-  InGroup<ImplicitFallthrough>, DefaultIgnore;
+  InGroup<ImplicitFallthroughUnreachable>, DefaultIgnore;
 
 def warn_unreachable_default : Warning<
   "default label in switch which covers all enumeration values">,
diff --git a/clang/test/SemaCXX/switch-implicit-fallthrough.cpp b/clang/test/SemaCXX/switch-implicit-fallthrough.cpp
--- a/clang/test/SemaCXX/switch-implicit-fallthrough.cpp
+++ b/clang/test/SemaCXX/switch-implicit-fallthrough.cpp
@@ -193,6 +193,28 @@
         ;
   }
 
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wimplicit-fallthrough-unreachable"
+  switch (n) {
+      n += 300;
+      [[clang::fallthrough]];  // no warning here
+    case 221:
+      return 1;
+      [[clang::fallthrough]];  // no warning here
+    case 222:
+      return 2;
+      __attribute__((fallthrough)); // no warning here
+    case 223:
+      if (1)
+        return 3;
+      __attribute__((fallthrough)); // no warning here
+    case 224:
+      n += 400;
+    case 225: // expected-warning{{unannotated fall-through between switch labels}} expected-note{{insert '[[clang::fallthrough]];' to silence this warning}} expected-note{{insert 'break;' to avoid fall-through}}
+        ;
+  }
+#pragma clang diagnostic pop
+
   long p = static_cast<long>(n) * n;
   switch (sizeof(p)) {
     case 9: