Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -10797,8 +10797,13 @@
 
     if (!FD->isInvalidDecl()) {
       // Don't diagnose unused parameters of defaulted or deleted functions.
-      if (!FD->isDeleted() && !FD->isDefaulted())
-        DiagnoseUnusedParameters(FD->param_begin(), FD->param_end());
+      if (!FD->isDeleted() && !FD->isDefaulted()) {
+        // Don't diagnose unused parameters in virtual methods or
+        // in methods that override base class methods.
+        const auto MD = dyn_cast<CXXMethodDecl>(FD);
+        if (!MD || (MD->size_overridden_methods() == 0U && !MD->isVirtual()))
+          DiagnoseUnusedParameters(FD->param_begin(), FD->param_end());
+      }
       DiagnoseSizeOfParametersAndReturnValue(FD->param_begin(), FD->param_end(),
                                              FD->getReturnType(), FD);
 
Index: test/SemaCXX/warn-unused-parameters.cpp
===================================================================
--- test/SemaCXX/warn-unused-parameters.cpp
+++ test/SemaCXX/warn-unused-parameters.cpp
@@ -32,3 +32,20 @@
   auto l = [&t...]() { return sizeof...(s); };
   return l();
 }
+
+// Don't diagnose virtual methods or methods that override base class
+// methods.
+class Base {
+public:
+  virtual void f(int x);
+};
+
+class Derived : public Base {
+public:
+  // Don't warn in overridden methods.
+  virtual void f(int x) {}
+
+  // Don't warn in virtual methods.
+  virtual void a(int x) {}
+};
+