Index: include/clang/AST/Type.h
===================================================================
--- include/clang/AST/Type.h
+++ include/clang/AST/Type.h
@@ -4901,7 +4901,9 @@
     return !isDependentType() || isCurrentInstantiation() || isTypeAlias();
   }
 
-  QualType desugar() const { return getCanonicalTypeInternal(); }
+  QualType desugar() const {
+    return isTypeAlias() ? getAliasedType() : getCanonicalTypeInternal();
+  }
 
   void Profile(llvm::FoldingSetNodeID &ID, const ASTContext &Ctx) {
     Profile(ID, Template, template_arguments(), Ctx);
Index: test/SemaCXX/alignof.cpp
===================================================================
--- test/SemaCXX/alignof.cpp
+++ test/SemaCXX/alignof.cpp
@@ -97,3 +97,8 @@
   typedef __attribute__((aligned(N))) int Field[sizeof(N)]; // expected-error {{requested alignment is dependent but declaration is not dependent}}
 };
 }
+
+typedef int __attribute__((aligned(16))) aligned_int;
+template <typename>
+using template_alias = aligned_int;
+static_assert(alignof(template_alias<void>) == 16, "Expected alignment of 16" );