Index: lib/Sema/SemaTemplate.cpp
===================================================================
--- lib/Sema/SemaTemplate.cpp
+++ lib/Sema/SemaTemplate.cpp
@@ -4804,7 +4804,12 @@
   // template.
   TemplateArgumentListInfo NewArgs = TemplateArgs;
 
-  TemplateParameterList *Params = Template->getTemplateParameters();
+  // Make sure we get the template parameter list from the most
+  // recentdeclaration, since that is the only one that has is guaranteed to
+  // have all the default template argument information.
+  TemplateParameterList *Params =
+      cast<TemplateDecl>(Template->getMostRecentDecl())
+          ->getTemplateParameters();
 
   SourceLocation RAngleLoc = NewArgs.getRAngleLoc();
 
Index: test/SemaCXX/template-default-param-through-using.cpp
===================================================================
--- test/SemaCXX/template-default-param-through-using.cpp
+++ test/SemaCXX/template-default-param-through-using.cpp
@@ -0,0 +1,33 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+// expected-no-diagnostics
+namespace llvm {
+  template<typename T > struct StringSet;
+  template<int I > struct Int;
+  template <typename Inner, template <typename> class Outer>
+    struct TemplTempl;
+}
+
+namespace lld {
+  using llvm::StringSet;
+  using llvm::Int;
+  using llvm::TemplTempl;
+};
+
+namespace llvm {
+  template<typename T > struct StringSet;
+}
+
+template<typename T> struct Temp{};
+
+namespace llvm {
+  template<typename T = int> struct StringSet{};
+  template<int I = 5> struct Int{};
+  template <typename Inner, template <typename> class Outer = Temp>
+    struct TemplTempl{};
+};
+
+namespace lld {
+  StringSet<> s;
+  Int<> i;
+  TemplTempl<int> tt;
+}