Index: lib/Serialization/ASTReaderDecl.cpp
===================================================================
--- lib/Serialization/ASTReaderDecl.cpp
+++ lib/Serialization/ASTReaderDecl.cpp
@@ -3788,9 +3788,31 @@
       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.
+      // FIXME: reduce the copy paste.
+      SmallVector<serialization::DeclID, 1> SpecID;
+      if (auto *CTD = dyn_cast<ClassTemplateDecl>(D)) {
+        SpecID.push_back(ReadDeclID());
+        auto *CommonPtr = CTD->getCommonPtr();
+        CommonPtr->LazySpecializations = newDeclIDList(
+            Reader.getContext(), CommonPtr->LazySpecializations, SpecID);
+
+      } else if (auto *FTD = dyn_cast<FunctionTemplateDecl>(D)) {
+        SpecID.push_back(ReadDeclID());
+        auto *CommonPtr = FTD->getCommonPtr();
+        CommonPtr->LazySpecializations = newDeclIDList(
+            Reader.getContext(), CommonPtr->LazySpecializations, SpecID);
+
+      } else if (auto *VTD = dyn_cast<VarTemplateDecl>(D)) {
+        SpecID.push_back(ReadDeclID());
+        auto *CommonPtr = VTD->getCommonPtr();
+        CommonPtr->LazySpecializations = newDeclIDList(
+            Reader.getContext(), CommonPtr->LazySpecializations, SpecID);
+
+      } else // TypeAliasTemplateDecl
+        assert(0 && "TypeAliasTemplateDecl doesn't have specs!");
+    }
       break;
 
     case UPD_CXX_ADDED_ANONYMOUS_NAMESPACE: {