Index: lib/Serialization/ASTReaderDecl.cpp
===================================================================
--- lib/Serialization/ASTReaderDecl.cpp
+++ lib/Serialization/ASTReaderDecl.cpp
@@ -206,6 +206,30 @@
                                                     DeclContext *DC);
     FindExistingResult findExisting(NamedDecl *D);
 
+    template <typename T>
+    void AddLazySpecializations(T *D,
+                                SmallVectorImpl<serialization::DeclID>& IDs) {
+      assert(!IDs.empty() && "no IDs to add to list");
+      assert(isa<RedeclarableTemplateDecl>(D) ||
+             isa<TypeAliasTemplateDecl>(D) &&
+             "Decl doesn't have specializations.");
+
+      auto *CommonPtr = D->getCommonPtr();
+      ASTContext &C = Reader.getContext();
+
+      if (auto &Old = CommonPtr->LazySpecializations) {
+        IDs.insert(IDs.end(), Old + 1, Old + 1 + Old[0]);
+        std::sort(IDs.begin(), IDs.end());
+        IDs.erase(std::unique(IDs.begin(), IDs.end()), IDs.end());
+      }
+
+      auto *Result = new (C) DeclID[1 + IDs.size()];
+      *Result = IDs.size();
+      std::copy(IDs.begin(), IDs.end(), Result + 1);
+
+      CommonPtr->LazySpecializations = Result;
+    }
+
   public:
     ASTDeclReader(ASTReader &Reader, ASTRecordReader &Record,
                   ASTReader::RecordLocation Loc,
@@ -1951,21 +1975,6 @@
   return Redecl;
 }
 
-static DeclID *newDeclIDList(ASTContext &Context, DeclID *Old,
-                             SmallVectorImpl<DeclID> &IDs) {
-  assert(!IDs.empty() && "no IDs to add to list");
-  if (Old) {
-    IDs.insert(IDs.end(), Old + 1, Old + 1 + Old[0]);
-    std::sort(IDs.begin(), IDs.end());
-    IDs.erase(std::unique(IDs.begin(), IDs.end()), IDs.end());
-  }
-
-  auto *Result = new (Context) DeclID[1 + IDs.size()];
-  *Result = IDs.size();
-  std::copy(IDs.begin(), IDs.end(), Result + 1);
-  return Result;
-}
-
 void ASTDeclReader::VisitClassTemplateDecl(ClassTemplateDecl *D) {
   RedeclarableResult Redecl = VisitRedeclarableTemplateDecl(D);
 
@@ -1975,11 +1984,8 @@
     SmallVector<serialization::DeclID, 32> SpecIDs;
     ReadDeclIDList(SpecIDs);
 
-    if (!SpecIDs.empty()) {
-      auto *CommonPtr = D->getCommonPtr();
-      CommonPtr->LazySpecializations = newDeclIDList(
-          Reader.getContext(), CommonPtr->LazySpecializations, SpecIDs);
-    }
+    if (!SpecIDs.empty())
+      AddLazySpecializations(D, SpecIDs);
   }
 
   if (D->getTemplatedDecl()->TemplateOrInstantiation) {
@@ -2007,11 +2013,8 @@
     SmallVector<serialization::DeclID, 32> SpecIDs;
     ReadDeclIDList(SpecIDs);
 
-    if (!SpecIDs.empty()) {
-      auto *CommonPtr = D->getCommonPtr();
-      CommonPtr->LazySpecializations = newDeclIDList(
-          Reader.getContext(), CommonPtr->LazySpecializations, SpecIDs);
-    }
+    if (!SpecIDs.empty())
+      AddLazySpecializations(D, SpecIDs);
   }
 }
 
@@ -2118,11 +2121,8 @@
     SmallVector<serialization::DeclID, 32> SpecIDs;
     ReadDeclIDList(SpecIDs);
 
-    if (!SpecIDs.empty()) {
-      auto *CommonPtr = D->getCommonPtr();
-      CommonPtr->LazySpecializations = newDeclIDList(
-          Reader.getContext(), CommonPtr->LazySpecializations, SpecIDs);
-    }
+    if (!SpecIDs.empty())
+      AddLazySpecializations(D, SpecIDs);
   }
 }
 
@@ -3908,9 +3908,19 @@
       break;
     }
 
-    case UPD_CXX_ADDED_TEMPLATE_SPECIALIZATION:
-      // It will be added to the template's specializations set when loaded.
-      (void)Record.readDecl();
+    case UPD_CXX_ADDED_TEMPLATE_SPECIALIZATION: {
+      // It will be added to the template's lazy specialization set when loaded.
+      SmallVector<serialization::DeclID, 1> SpecID;
+      SpecID.push_back(ReadDeclID());
+      if (auto *CTD = dyn_cast<ClassTemplateDecl>(D))
+        AddLazySpecializations(CTD, SpecID);
+      else if (auto *FTD = dyn_cast<FunctionTemplateDecl>(D))
+        AddLazySpecializations(FTD, SpecID);
+      else if (auto *VTD = dyn_cast<VarTemplateDecl>(D))
+        AddLazySpecializations(VTD, SpecID);
+      else // TypeAliasTemplateDecl
+        llvm_unreachable("TypeAliasTemplateDecl doesn't have specs!");
+    }
       break;
 
     case UPD_CXX_ADDED_ANONYMOUS_NAMESPACE: {