diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -14210,6 +14210,9 @@
   if (!FD->isGlobal())
     return false;
 
+  if (!FD->isExternallyVisible())
+    return false;
+
   // Don't warn about C++ member functions.
   if (isa<CXXMethodDecl>(FD))
     return false;
diff --git a/clang/test/SemaCXX/warn-missing-prototypes.cpp b/clang/test/SemaCXX/warn-missing-prototypes.cpp
--- a/clang/test/SemaCXX/warn-missing-prototypes.cpp
+++ b/clang/test/SemaCXX/warn-missing-prototypes.cpp
@@ -44,3 +44,16 @@
 extern void k() {} // expected-warning {{no previous prototype for function 'k'}}
 // expected-note@-1{{declare 'static' if the function is not intended to be used outside of this translation unit}}
 // CHECK-NOT: fix-it:"{{.*}}":{[[@LINE-2]]:{{.*}}-[[@LINE-2]]:{{.*}}}:"{{.*}}"
+
+namespace {
+struct anon { };
+}
+
+// No warning because this has internal linkage despite not being declared
+// explicitly 'static', owing to the internal linkage parameter.
+void l(anon) {
+}
+
+void *operator new(decltype(sizeof(3)) size, const anon &) throw() {
+  return nullptr;
+}