Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -2109,6 +2109,9 @@
   "definition of dllimport data">;
 def err_attribute_dllimport_static_field_definition : Error<
   "definition of dllimport static field not allowed">;
+def warn_attribute_dllimport_static_field_definition : Warning<
+  "definition of dllimport static field">,
+  InGroup<DiagGroup<"dllimport-static-field-def">>;
 def err_attribute_dll_member_of_dll_class : Error<
   "attribute %q0 cannot be applied to member of %q1 class">;
 def err_attribute_weakref_not_static : Error<
Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -9061,10 +9061,17 @@
   if (const DLLImportAttr *IA = VD->getAttr<DLLImportAttr>()) {
     if (VD->isStaticDataMember() && VD->isOutOfLine() &&
         VD->isThisDeclarationADefinition()) {
+      // We allow definitions of dllimport class template static data members
+      // with a warning.
+      bool JustWarn = cast<CXXRecordDecl>(VD->getFirstDecl()->getDeclContext())
+                          ->getDescribedClassTemplate();
+
       Diag(VD->getLocation(),
-           diag::err_attribute_dllimport_static_field_definition);
+           JustWarn ? diag::warn_attribute_dllimport_static_field_definition
+                    : diag::err_attribute_dllimport_static_field_definition);
       Diag(IA->getLocation(), diag::note_attribute);
-      VD->setInvalidDecl();
+      if (!JustWarn)
+        VD->setInvalidDecl();
     }
   }
 
Index: test/CodeGenCXX/dllimport.cpp
===================================================================
--- test/CodeGenCXX/dllimport.cpp
+++ test/CodeGenCXX/dllimport.cpp
@@ -571,6 +571,15 @@
   template class C<char>;
 }
 
+namespace ClassTemplateStaticDef {
+  template <typename T> struct __declspec(dllimport) S {
+    static int x;
+  };
+  template <typename T> int S<T>::x;
+  // CHECK-DAG: @"\01?x@?$S@H@ClassTemplateStaticDef@@2HA" = available_externally dllimport global i32 0
+  int f() { return S<int>::x; }
+}
+
 //===----------------------------------------------------------------------===//
 // Negative checks
 //===----------------------------------------------------------------------===//
Index: test/SemaCXX/dllimport.cpp
===================================================================
--- test/SemaCXX/dllimport.cpp
+++ test/SemaCXX/dllimport.cpp
@@ -816,9 +816,9 @@
 template<typename T> inline void ImportClassTmplMembers<T>::staticInlineDef() {}
 template<typename T>        void ImportClassTmplMembers<T>::staticInlineDecl() {}
 
-template<typename T>        int  ImportClassTmplMembers<T>::StaticFieldDef; // expected-error{{definition of dllimport static field not allowed}}
-template<typename T> const  int  ImportClassTmplMembers<T>::StaticConstFieldDef = 1; // expected-error{{definition of dllimport static field not allowed}}
-template<typename T> constexpr int ImportClassTmplMembers<T>::ConstexprFieldDef; // expected-error{{definition of dllimport static field not allowed}}
+template<typename T>        int  ImportClassTmplMembers<T>::StaticFieldDef; // expected-warning{{definition of dllimport static field}}
+template<typename T> const  int  ImportClassTmplMembers<T>::StaticConstFieldDef = 1; // expected-warning{{definition of dllimport static field}}
+template<typename T> constexpr int ImportClassTmplMembers<T>::ConstexprFieldDef; // expected-warning{{definition of dllimport static field}}
 
 
 // Redeclarations cannot add dllimport.
@@ -853,13 +853,13 @@
 template<typename T> __declspec(dllimport)        void CTMR<T>::staticInlineDecl() {}  // expected-error{{redeclaration of 'CTMR::staticInlineDecl' cannot add 'dllimport' attribute}}
 
 template<typename T> __declspec(dllimport)        int  CTMR<T>::StaticField = 1;       // expected-error{{redeclaration of 'CTMR::StaticField' cannot add 'dllimport' attribute}}
-                                                                                       // expected-error@-1{{definition of dllimport static field not allowed}}
+                                                                                       // expected-warning@-1{{definition of dllimport static field}}
                                                                                        // expected-note@-2{{attribute is here}}
 template<typename T> __declspec(dllimport) const  int  CTMR<T>::StaticConstField = 1;  // expected-error{{redeclaration of 'CTMR::StaticConstField' cannot add 'dllimport' attribute}}
-                                                                                       // expected-error@-1{{definition of dllimport static field not allowed}}
+                                                                                       // expected-warning@-1{{definition of dllimport static field}}
                                                                                        // expected-note@-2{{attribute is here}}
 template<typename T> __declspec(dllimport) constexpr int CTMR<T>::ConstexprField;      // expected-error{{redeclaration of 'CTMR::ConstexprField' cannot add 'dllimport' attribute}}
-                                                                                       // expected-error@-1{{definition of dllimport static field not allowed}}
+                                                                                       // expected-warning@-1{{definition of dllimport static field}}
                                                                                        // expected-note@-2{{attribute is here}}
 
 
@@ -901,9 +901,9 @@
 template<typename T> template<typename U>        void ImportClsTmplMemTmpl<T>::staticInlineDecl() {}
 
 #if __has_feature(cxx_variable_templates)
-template<typename T> template<typename U>        int  ImportClsTmplMemTmpl<T>::StaticFieldDef; // expected-error{{definition of dllimport static field not allowed}}
-template<typename T> template<typename U> const  int  ImportClsTmplMemTmpl<T>::StaticConstFieldDef = 1; // expected-error{{definition of dllimport static field not allowed}}
-template<typename T> template<typename U> constexpr int ImportClsTmplMemTmpl<T>::ConstexprFieldDef; // expected-error{{definition of dllimport static field not allowed}}
+template<typename T> template<typename U>        int  ImportClsTmplMemTmpl<T>::StaticFieldDef; // expected-warning{{definition of dllimport static field}}
+template<typename T> template<typename U> const  int  ImportClsTmplMemTmpl<T>::StaticConstFieldDef = 1; // expected-warning{{definition of dllimport static field}}
+template<typename T> template<typename U> constexpr int ImportClsTmplMemTmpl<T>::ConstexprFieldDef; // expected-warning{{definition of dllimport static field}}
 #endif // __has_feature(cxx_variable_templates)
 
 
@@ -935,13 +935,13 @@
 
 #if __has_feature(cxx_variable_templates)
 template<typename T> template<typename U> __declspec(dllimport)        int  CTMTR<T>::StaticField = 1;       // expected-error{{redeclaration of 'CTMTR::StaticField' cannot add 'dllimport' attribute}}
-                                                                                                             // expected-error@-1{{definition of dllimport static field not allowed}}
+                                                                                                             // expected-warning@-1{{definition of dllimport static field}}
                                                                                                              // expected-note@-2{{attribute is here}}
 template<typename T> template<typename U> __declspec(dllimport) const  int  CTMTR<T>::StaticConstField = 1;  // expected-error{{redeclaration of 'CTMTR::StaticConstField' cannot add 'dllimport' attribute}}
-                                                                                                             // expected-error@-1{{definition of dllimport static field not allowed}}
+                                                                                                             // expected-warning@-1{{definition of dllimport static field}}
                                                                                                              // expected-note@-2{{attribute is here}}
 template<typename T> template<typename U> __declspec(dllimport) constexpr int CTMTR<T>::ConstexprField;      // expected-error{{redeclaration of 'CTMTR::ConstexprField' cannot add 'dllimport' attribute}}
-                                                                                                             // expected-error@-1{{definition of dllimport static field not allowed}}
+                                                                                                             // expected-warning@-1{{definition of dllimport static field}}
                                                                                                              // expected-note@-2{{attribute is here}}
 #endif // __has_feature(cxx_variable_templates)
 
@@ -976,3 +976,10 @@
   void __declspec(dllimport) foo();
   void __declspec(dllexport) bar();
 };
+
+namespace ImportedExplicitSpecialization {
+template <typename T> struct S { static int x; };
+template <typename T> int S<T>::x = sizeof(T);
+template <> struct __declspec(dllimport) S<int> { static int x; }; // expected-note{{attribute is here}}
+int S<int>::x = -1; // expected-error{{definition of dllimport static field not allowed}}
+}