Index: clang/lib/AST/ASTImporter.cpp
===================================================================
--- clang/lib/AST/ASTImporter.cpp
+++ clang/lib/AST/ASTImporter.cpp
@@ -5158,7 +5158,7 @@
   // context. This context will be fixed when the actual template declaration
   // is created.
 
-  // FIXME: Import default argument  and constraint expression.
+  // FIXME: Import constraint expression.
 
   ExpectedSLoc BeginLocOrErr = import(D->getBeginLoc());
   if (!BeginLocOrErr)
@@ -5206,6 +5206,14 @@
         ToIDC);
   }
 
+  if (D->hasDefaultArgument()) {
+    Expected<TypeSourceInfo *> ToDefaultArgOrErr =
+        import(D->getDefaultArgumentInfo());
+    if (!ToDefaultArgOrErr)
+      return ToDefaultArgOrErr.takeError();
+    ToD->setDefaultArgument(*ToDefaultArgOrErr);
+  }
+
   return ToD;
 }
 
Index: clang/unittests/AST/ASTImporterTest.cpp
===================================================================
--- clang/unittests/AST/ASTImporterTest.cpp
+++ clang/unittests/AST/ASTImporterTest.cpp
@@ -880,6 +880,25 @@
                  has(fieldDecl(hasType(dependentSizedArrayType())))))));
 }
 
+TEST_P(ASTImporterOptionSpecificTestBase, TemplateTypeParmDeclNoDefaultArg) {
+  Decl *FromTU = getTuDecl("template<typename T> struct X {};", Lang_CXX03);
+  auto From = FirstDeclMatcher<TemplateTypeParmDecl>().match(
+      FromTU, templateTypeParmDecl(hasName("T")));
+  TemplateTypeParmDecl *To = Import(From, Lang_CXX03);
+  ASSERT_FALSE(To->hasDefaultArgument());
+}
+
+TEST_P(ASTImporterOptionSpecificTestBase, TemplateTypeParmDeclDefaultArg) {
+  Decl *FromTU =
+      getTuDecl("template<typename T = int> struct X {};", Lang_CXX03);
+  auto From = FirstDeclMatcher<TemplateTypeParmDecl>().match(
+      FromTU, templateTypeParmDecl(hasName("T")));
+  TemplateTypeParmDecl *To = Import(From, Lang_CXX03);
+  ASSERT_TRUE(To->hasDefaultArgument());
+  QualType ToArg = To->getDefaultArgument();
+  ASSERT_EQ(ToArg, QualType(To->getASTContext().IntTy));
+}
+
 TEST_P(ASTImporterOptionSpecificTestBase, ImportBeginLocOfDeclRefExpr) {
   Decl *FromTU =
       getTuDecl("class A { public: static int X; }; void f() { (void)A::X; }",