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
@@ -1358,7 +1358,8 @@
   Expected<TypedefNameDecl *> ToDeclOrErr = import(T->getDecl());
   if (!ToDeclOrErr)
     return ToDeclOrErr.takeError();
-  ExpectedType ToUnderlyingTypeOrErr = import(T->desugar());
+  ExpectedType ToUnderlyingTypeOrErr =
+      import(QualType(T, 0).getDesugaredType(T->getDecl()->getASTContext()));
   if (!ToUnderlyingTypeOrErr)
     return ToUnderlyingTypeOrErr.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
@@ -8075,6 +8075,36 @@
   EXPECT_FALSE(SharedStatePtr->isNewDecl(ToBar));
 }
 
+TEST_P(ASTImporterOptionSpecificTestBase, isSugaredImport) {
+  Decl *FromTU = getTuDecl(
+      R"(
+      typedef __builtin_va_list va_list;
+      void dbgout(char* fmt, ...)
+      {
+        va_list va;
+      } 
+      )",
+      Lang_C99);
+  Decl *ToTU = getToTuDecl(
+      R"(
+      typedef __builtin_va_list va_list;
+      void dbgout(char* fmt, ...);
+      void maindbgout(char* str)
+      {
+        dbgout((char*)str);
+      }
+      )",
+      Lang_C99);
+  auto *FromOther = FirstDeclMatcher<FunctionDecl>().match(
+      FromTU, functionDecl(hasName("dbgout")));
+  ASSERT_TRUE(FromOther);
+
+  auto *ToOther = Import(FromOther, Lang_C99);
+  ASSERT_TRUE(ToOther);
+
+  // EXPECT_TRUE(SharedStatePtr->isSugaredImport(ToOther));
+}
+
 INSTANTIATE_TEST_SUITE_P(ParameterizedTests, ASTImporterLookupTableTest,
                          DefaultTestValuesForRunOptions);