Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -510,6 +510,7 @@
 def err_main_arg_wrong : Error<"%select{first|second|third|fourth}0 "
     "parameter of 'main' (%select{argument count|argument array|environment|"
     "platform-specific data}0) must be of type %1">;
+def err_main_global_variable : Error<"main can't be declared as global variable">;
 def ext_main_used : Extension<
   "ISO C++ does not allow 'main' to be used by a program">, InGroup<Main>;
 
Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -6105,6 +6105,13 @@
     }
   }
 
+  // [basic.start.main]p3
+  // A program that declares a variable main at global scope is ill-formed.
+  if (getLangOpts().CPlusPlus && Name.getAsString() == "main" &&
+      NewVD->isFileVarDecl()) {
+      Diag(D.getLocStart(), diag::err_main_global_variable);
+  }
+
   if (D.isRedeclaration() && !Previous.empty()) {
     checkDLLAttributeRedeclaration(
         *this, dyn_cast<NamedDecl>(Previous.getRepresentativeDecl()), NewVD,
Index: test/CXX/basic/basic.start/basic.start.main/p3.cpp
===================================================================
--- test/CXX/basic/basic.start/basic.start.main/p3.cpp
+++ test/CXX/basic/basic.start/basic.start.main/p3.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+int main; // expected-error{{main can't be declared as global variable}}
+
+int f () {
+  int main; // OK
+  (void)main;
+}