diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -836,7 +836,8 @@
     ExpectedType ToTypeOrErr = import(From.getAsType());
     if (!ToTypeOrErr)
       return ToTypeOrErr.takeError();
-    return TemplateArgument(*ToTypeOrErr);
+    return TemplateArgument(*ToTypeOrErr, /*isNullPtr*/ false,
+                            From.getIsDefaulted());
   }
 
   case TemplateArgument::Integral: {
@@ -853,14 +854,15 @@
     ExpectedType ToTypeOrErr = import(From.getParamTypeForDecl());
     if (!ToTypeOrErr)
       return ToTypeOrErr.takeError();
-    return TemplateArgument(*ToOrErr, *ToTypeOrErr);
+    return TemplateArgument(*ToOrErr, *ToTypeOrErr, From.getIsDefaulted());
   }
 
   case TemplateArgument::NullPtr: {
     ExpectedType ToTypeOrErr = import(From.getNullPtrType());
     if (!ToTypeOrErr)
       return ToTypeOrErr.takeError();
-    return TemplateArgument(*ToTypeOrErr, /*isNullPtr*/true);
+    return TemplateArgument(*ToTypeOrErr, /*isNullPtr*/ true,
+                            From.getIsDefaulted());
   }
 
   case TemplateArgument::Template: {
@@ -868,7 +870,7 @@
     if (!ToTemplateOrErr)
       return ToTemplateOrErr.takeError();
 
-    return TemplateArgument(*ToTemplateOrErr);
+    return TemplateArgument(*ToTemplateOrErr, From.getIsDefaulted());
   }
 
   case TemplateArgument::TemplateExpansion: {
@@ -877,13 +879,13 @@
     if (!ToTemplateOrErr)
       return ToTemplateOrErr.takeError();
 
-    return TemplateArgument(
-        *ToTemplateOrErr, From.getNumTemplateExpansions());
+    return TemplateArgument(*ToTemplateOrErr, From.getNumTemplateExpansions(),
+                            From.getIsDefaulted());
   }
 
   case TemplateArgument::Expression:
     if (ExpectedExpr ToExpr = import(From.getAsExpr()))
-      return TemplateArgument(*ToExpr);
+      return TemplateArgument(*ToExpr, From.getIsDefaulted());
     else
       return ToExpr.takeError();
 
diff --git a/clang/unittests/AST/ASTImporterTest.cpp b/clang/unittests/AST/ASTImporterTest.cpp
--- a/clang/unittests/AST/ASTImporterTest.cpp
+++ b/clang/unittests/AST/ASTImporterTest.cpp
@@ -1158,6 +1158,26 @@
   ASSERT_EQ(cast<IntegerLiteral>(ToArg)->getValue().getLimitedValue(), 1U);
 }
 
+TEST_P(ASTImporterOptionSpecificTestBase, TemplateArgumentsDefaulted) {
+  Decl *FromTU = getTuDecl(R"(
+                           template<typename T> struct X {};
+                           template<typename TP = double,
+                                    int NTTP = 50,
+                                    template<typename> typename TT = X> struct S {};
+                           S<> s;
+                           )",
+                           Lang_CXX17);
+  auto *FromSpec = FirstDeclMatcher<ClassTemplateSpecializationDecl>().match(
+      FromTU, classTemplateSpecializationDecl(hasName("S")));
+  ASSERT_TRUE(FromSpec);
+  auto *ToSpec = Import(FromSpec, Lang_CXX03);
+  ASSERT_TRUE(ToSpec);
+  auto const &TList = ToSpec->getTemplateArgs();
+  for (auto const &Arg : TList.asArray()) {
+    ASSERT_TRUE(Arg.getIsDefaulted());
+  }
+}
+
 TEST_P(ASTImporterOptionSpecificTestBase,
        ImportOfTemplatedDeclOfClassTemplateDecl) {
   Decl *FromTU = getTuDecl("template<class X> struct S{};", Lang_CXX03);