diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index b67dfb8e3424..8859cc1b67d7 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -1356,11 +1356,23 @@ static void propagateDLLAttrToBaseClassTemplate(
     return;
   }
 
-  if (BaseTemplateSpec->getSpecializationKind() == TSK_Undeclared) {
-    // If the base class is not already specialized, we can do the propagation.
+  auto TSK = BaseTemplateSpec->getSpecializationKind();
+  if (!getDLLAttr(BaseTemplateSpec) &&
+      (TSK == TSK_Undeclared || TSK == TSK_ExplicitInstantiationDeclaration ||
+       TSK == TSK_ImplicitInstantiation)) {
+    // The template hasn't been instantiated yet (or it has, but only as an
+    // explicit instantiation declaration or implicit instantiation, which means
+    // we haven't codegenned any members yet), so propagate the attribute.
     auto *NewAttr = cast<InheritableAttr>(ClassAttr->clone(S.getASTContext()));
     NewAttr->setInherited(true);
     BaseTemplateSpec->addAttr(NewAttr);
+
+    // If the template is already instantiated, checkDLLAttributeRedeclaration()
+    // needs to be run again to work see the new attribute. Otherwise this will
+    // get run whenever the template is instantiated.
+    if (TSK != TSK_Undeclared)
+      S.checkClassLevelDLLAttribute(BaseTemplateSpec);
+
     return;
   }
 
@@ -4783,8 +4795,9 @@ void Sema::checkClassLevelDLLAttribute(CXXRecordDecl *Class) {
 
   TemplateSpecializationKind TSK = Class->getTemplateSpecializationKind();
 
-  // Don't dllexport explicit class template instantiation declarations.
-  if (ClassExported && TSK == TSK_ExplicitInstantiationDeclaration) {
+  // Ignore explicit dllexport on explicit class template instantiation declarations.
+  if (ClassExported && !ClassAttr->isInherited() &&
+      TSK == TSK_ExplicitInstantiationDeclaration) {
     Class->dropAttr<DLLExportAttr>();
     return;
   }
@@ -4832,12 +4845,15 @@ void Sema::checkClassLevelDLLAttribute(CXXRecordDecl *Class) {
     }
 
     if (MD && ClassExported) {
+      if (TSK == TSK_ExplicitInstantiationDeclaration)
+        // Don't go any further if this is just an explicit instantiation
+        // declaration.
+        continue;
+
       if (MD->isUserProvided()) {
         // Instantiate non-default class member functions ...
 
         // .. except for certain kinds of template specializations.
-        if (TSK == TSK_ExplicitInstantiationDeclaration)
-          continue;
         if (TSK == TSK_ImplicitInstantiation && !ClassAttr->isInherited())
           continue;
 
diff --git a/clang/test/CodeGenCXX/dllexport.cpp b/clang/test/CodeGenCXX/dllexport.cpp
index 916e69500529..33df96402252 100644
--- a/clang/test/CodeGenCXX/dllexport.cpp
+++ b/clang/test/CodeGenCXX/dllexport.cpp
@@ -755,11 +755,11 @@ USEMEMFUNC(DerivedFromImportedTemplate, func)
 // M32-DAG: {{declare|define available_externally}} dllimport x86_thiscallcc void @"\01?func@?$ImportedClassTemplate@H@@QAEXXZ"
 // G32-DAG: declare dllimport x86_thiscallcc void @_ZN21ImportedClassTemplateIiE4funcEv
 
-// Base class already instantiated without dll attribute.
+// Base class already implicitly instantiated without dll attribute.
 struct DerivedFromTemplateD : public ClassTemplate<double> {};
 struct __declspec(dllexport) DerivedFromTemplateD2 : public ClassTemplate<double> {};
 USEMEMFUNC(DerivedFromTemplateD2, func)
-// M32-DAG: define linkonce_odr x86_thiscallcc void @"\01?func@?$ClassTemplate@N@@QAEXXZ"
+// M32-DAG: define weak_odr dllexport x86_thiscallcc void @"\01?func@?$ClassTemplate@N@@QAEXXZ"
 // G32-DAG: define linkonce_odr x86_thiscallcc void @_ZN13ClassTemplateIdE4funcEv
 
 // MS: Base class already instantiated with different dll attribute.
@@ -812,3 +812,18 @@ struct __declspec(dllexport) BottomClass : public MiddleClass<int> { };
 USEMEMFUNC(BottomClass, func)
 // M32-DAG: define weak_odr dllexport x86_thiscallcc void @"\01?func@?$TopClass@H@@QAEXXZ"
 // G32-DAG: define linkonce_odr x86_thiscallcc void @_ZN8TopClassIiE4funcEv
+
+template <typename T> struct ExplicitInstantiationDeclTemplateBase { void func() {} };
+extern template struct ExplicitInstantiationDeclTemplateBase<int>;
+struct __declspec(dllexport) DerivedFromExplicitInstantiationDeclTemplateBase : public ExplicitInstantiationDeclTemplateBase<int> {};
+template struct ExplicitInstantiationDeclTemplateBase<int>;
+// M32-DAG: define weak_odr dllexport x86_thiscallcc void @"\01?func@?$ExplicitInstantiationDeclTemplateBase@H@@QAEXXZ"
+// G32-DAG: define weak_odr x86_thiscallcc void @_ZN37ExplicitInstantiationDeclTemplateBaseIiE4funcEv
+
+template <typename T> struct ExplicitInstantiationDeclTemplateBase2 { void func() {} };
+extern template struct ExplicitInstantiationDeclTemplateBase2<int>;
+struct __declspec(dllexport) DerivedFromExplicitInstantiationDeclTemplateBase2 : public ExplicitInstantiationDeclTemplateBase2<int> {};
+template struct __declspec(dllimport) ExplicitInstantiationDeclTemplateBase2<int>;
+USEMEMFUNC(ExplicitInstantiationDeclTemplateBase2<int>, func)
+// M32-DAG: define weak_odr dllexport x86_thiscallcc void @"\01?func@?$ExplicitInstantiationDeclTemplateBase2@H@@QAEXXZ"
+// G32-DAG: define weak_odr x86_thiscallcc void @_ZN38ExplicitInstantiationDeclTemplateBase2IiE4funcEv
diff --git a/clang/test/CodeGenCXX/dllimport.cpp b/clang/test/CodeGenCXX/dllimport.cpp
index 0867fdd3f037..779a27816eab 100644
--- a/clang/test/CodeGenCXX/dllimport.cpp
+++ b/clang/test/CodeGenCXX/dllimport.cpp
@@ -785,11 +785,11 @@ USEMEMFUNC(ExportedClassTemplate<int>, func)
 // M32-DAG: define weak_odr dllexport x86_thiscallcc void @"\01?func@?$ExportedClassTemplate@H@@QAEXXZ"
 // G32-DAG: define weak_odr dllexport x86_thiscallcc void @_ZN21ExportedClassTemplateIiE4funcEv
 
-// Base class already instantiated without attribute.
+// Base class already implicitly instantiated without attribute.
 struct DerivedFromTemplateD : public ClassTemplate<double> {};
 struct __declspec(dllimport) DerivedFromTemplateD2 : public ClassTemplate<double> {};
 USEMEMFUNC(ClassTemplate<double>, func)
-// M32-DAG: define linkonce_odr x86_thiscallcc void @"\01?func@?$ClassTemplate@N@@QAEXXZ"
+// M32-DAG: declare dllimport x86_thiscallcc void @"\01?func@?$ClassTemplate@N@@QAEXXZ"
 // G32-DAG: define linkonce_odr x86_thiscallcc void @_ZN13ClassTemplateIdE4funcEv
 
 // MS: Base class already instantiated with dfferent attribute.
@@ -842,3 +842,19 @@ struct __declspec(dllimport) BottomClass : public MiddleClass<int> { };
 USEMEMFUNC(TopClass<int>, func)
 // M32-DAG: {{declare|define available_externally}} dllimport x86_thiscallcc void @"\01?func@?$TopClass@H@@QAEXXZ"
 // G32-DAG: define linkonce_odr x86_thiscallcc void @_ZN8TopClassIiE4funcEv
+
+template <typename T> struct ExplicitInstantiationDeclTemplateBase { void func() {} };
+extern template struct ExplicitInstantiationDeclTemplateBase<int>;
+struct __declspec(dllimport) DerivedFromExplicitInstantiationDeclTemplateBase : public ExplicitInstantiationDeclTemplateBase<int> {};
+template struct ExplicitInstantiationDeclTemplateBase<int>;
+USEMEMFUNC(ExplicitInstantiationDeclTemplateBase<int>, func)
+// M32-DAG: declare dllimport x86_thiscallcc void @"\01?func@?$ExplicitInstantiationDeclTemplateBase@H@@QAEXXZ"
+// G32-DAG: define weak_odr x86_thiscallcc void @_ZN37ExplicitInstantiationDeclTemplateBaseIiE4funcEv
+
+template <typename T> struct ExplicitInstantiationDeclTemplateBase2 { void func() {} };
+extern template struct ExplicitInstantiationDeclTemplateBase2<int>;
+struct __declspec(dllimport) DerivedFromExplicitInstantiationDeclTemplateBase2 : public ExplicitInstantiationDeclTemplateBase2<int> {};
+template struct __declspec(dllexport) ExplicitInstantiationDeclTemplateBase2<int>;
+USEMEMFUNC(ExplicitInstantiationDeclTemplateBase2<int>, func)
+// M32-DAG: declare dllimport x86_thiscallcc void @"\01?func@?$ExplicitInstantiationDeclTemplateBase2@H@@QAEXXZ"
+// G32-DAG: define weak_odr x86_thiscallcc void @_ZN38ExplicitInstantiationDeclTemplateBase2IiE4funcEv
diff --git a/clang/test/SemaCXX/dllexport.cpp b/clang/test/SemaCXX/dllexport.cpp
index a6009f93c8d6..badb9e259597 100644
--- a/clang/test/SemaCXX/dllexport.cpp
+++ b/clang/test/SemaCXX/dllexport.cpp
@@ -439,14 +439,14 @@ class __declspec(dllexport) DerivedFromExportedTemplate : public ExportedClassTe
 // ImportedTemplate is explicitly imported.
 class __declspec(dllexport) DerivedFromImportedTemplate : public ImportedClassTemplate<int> {};
 
-#ifdef MS
-// expected-note@+4{{class template 'ClassTemplate<double>' was instantiated here}}
-// expected-warning@+4{{propagating dll attribute to already instantiated base class template without dll attribute is not supported}}
-// expected-note@+3{{attribute is here}}
-#endif
 class DerivedFromTemplateD : public ClassTemplate<double> {};
+// Base class previously implicitly instantiated without attribute; it will get propagated.
 class __declspec(dllexport) DerivedFromTemplateD2 : public ClassTemplate<double> {};
 
+// Base class has explicit instantiation declaration; the attribute will get propagated.
+extern template class ClassTemplate<float>;
+class __declspec(dllexport) DerivedFromTemplateF : public ClassTemplate<float> {};
+
 class __declspec(dllexport) DerivedFromTemplateB : public ClassTemplate<bool> {};
 // The second derived class doesn't change anything, the attribute that was propagated first wins.
 class __declspec(dllimport) DerivedFromTemplateB2 : public ClassTemplate<bool> {};
@@ -475,6 +475,10 @@ struct __declspec(dllexport) DerivedFromExplicitlyExportInstantiatedTemplate : p
 // Base class already instantiated with import attribute.
 struct __declspec(dllexport) DerivedFromExplicitlyImportInstantiatedTemplate : public ExplicitlyImportInstantiatedTemplate<int> {};
 
+template <typename T> struct ExplicitInstantiationDeclTemplateBase { void func() {} };
+extern template struct ExplicitInstantiationDeclTemplateBase<int>;
+struct __declspec(dllexport) DerivedFromExplicitInstantiationDeclTemplateBase : public ExplicitInstantiationDeclTemplateBase<int> {};
+
 
 //===----------------------------------------------------------------------===//
 // Precedence
diff --git a/clang/test/SemaCXX/dllimport.cpp b/clang/test/SemaCXX/dllimport.cpp
index 62d4f7b57590..0f616d43c89d 100644
--- a/clang/test/SemaCXX/dllimport.cpp
+++ b/clang/test/SemaCXX/dllimport.cpp
@@ -1274,14 +1274,14 @@ class __declspec(dllimport) DerivedFromImportedTemplate : public ImportedClassTe
 // ExportedClassTemplate is explicitly exported.
 class __declspec(dllimport) DerivedFromExportedTemplate : public ExportedClassTemplate<int> {};
 
-#ifdef MS
-// expected-note@+4{{class template 'ClassTemplate<double>' was instantiated here}}
-// expected-warning@+4{{propagating dll attribute to already instantiated base class template without dll attribute is not supported}}
-// expected-note@+3{{attribute is here}}
-#endif
 class DerivedFromTemplateD : public ClassTemplate<double> {};
+// Base class previously implicitly instantiated without attribute; it will get propagated.
 class __declspec(dllimport) DerivedFromTemplateD2 : public ClassTemplate<double> {};
 
+// Base class has explicit instantiation declaration; the attribute will get propagated.
+extern template class ClassTemplate<float>;
+class __declspec(dllimport) DerivedFromTemplateF : public ClassTemplate<float> {};
+
 class __declspec(dllimport) DerivedFromTemplateB : public ClassTemplate<bool> {};
 // The second derived class doesn't change anything, the attribute that was propagated first wins.
 class __declspec(dllexport) DerivedFromTemplateB2 : public ClassTemplate<bool> {};
@@ -1329,3 +1329,7 @@ struct __declspec(dllimport) DerivedFromExplicitlyExportInstantiatedTemplate : p
 
 // Base class already instantiated with import attribute.
 struct __declspec(dllimport) DerivedFromExplicitlyImportInstantiatedTemplate : public ExplicitlyImportInstantiatedTemplate<int> {};
+
+template <typename T> struct ExplicitInstantiationDeclTemplateBase { void func() {} };
+extern template struct ExplicitInstantiationDeclTemplateBase<int>;
+struct __declspec(dllimport) DerivedFromExplicitInstantiationDeclTemplateBase : public ExplicitInstantiationDeclTemplateBase<int> {};