diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 573ae97bff710..400d447518c73 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -767,6 +767,7 @@ Bug Fixes to C++ Support
 - Clang could incorrectly instantiate functions in discarded contexts (#GH140449)
 - Fix instantiation of default-initialized variable template specialization. (#GH140632) (#GH140622)
 - Clang modules now allow a module and its user to differ on TrivialAutoVarInit*
+- Fixed an access checking bug when initializing non-aggregates in default arguments (#GH62444), (#GH83608)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index d028eea4f8f3e..cd20dfb4fe093 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -3340,13 +3340,13 @@ bool Sema::SubstDefaultArgument(
   }
 
   ExprResult Result;
+  // C++ [dcl.fct.default]p5:
+  //   The names in the [default argument] expression are bound, and
+  //   the semantic constraints are checked, at the point where the
+  //   default argument expression appears.
+  ContextRAII SavedContext(*this, FD);
   {
-    // C++ [dcl.fct.default]p5:
-    //   The names in the [default argument] expression are bound, and
-    //   the semantic constraints are checked, at the point where the
-    //   default argument expression appears.
-    ContextRAII SavedContext(*this, FD);
-    std::unique_ptr<LocalInstantiationScope> LIS;
+    std::optional<LocalInstantiationScope> LIS;
 
     if (ForCallExpr) {
       // When instantiating a default argument due to use in a call expression,
@@ -3354,7 +3354,7 @@ bool Sema::SubstDefaultArgument(
       // required to satisfy references from the default argument. For example:
       //   template<typename T> void f(T a, int = decltype(a)());
       //   void g() { f(0); }
-      LIS = std::make_unique<LocalInstantiationScope>(*this);
+      LIS.emplace(*this);
       FunctionDecl *PatternFD = FD->getTemplateInstantiationPattern(
           /*ForDefinition*/ false);
       if (addInstantiatedParametersToScope(FD, PatternFD, *LIS, TemplateArgs))
diff --git a/clang/test/SemaCXX/access-control-check.cpp b/clang/test/SemaCXX/access-control-check.cpp
index 4540e99d8a337..76d27ce3e55cb 100644
--- a/clang/test/SemaCXX/access-control-check.cpp
+++ b/clang/test/SemaCXX/access-control-check.cpp
@@ -13,3 +13,49 @@ class N : M,P {
   N() {}
   int PR() { return iP + PPR(); } // expected-error 2 {{private member of 'P'}}
 };
+
+namespace GH83608 {
+
+class single;
+
+class check_constructible {
+  // This makes the class a non-aggregate, which enforces us to check
+  // the constructor when initializing.
+  check_constructible() {}
+
+  friend class single;
+};
+
+struct single {
+  template <class T> single(T u, check_constructible = {}) {}
+};
+
+// We perform access checking when substituting into the default argument.
+// Make sure it runs within the context of 'single'.
+single x(0);
+
+}
+
+namespace GH62444 {
+
+struct B {
+  friend struct A;
+private:
+  B(int); // #B
+};
+
+template<class T>
+int f(T = 0); // #Decl
+
+struct A {
+  A() {
+    int i = f<B>();
+    // expected-error@#Decl {{calling a private constructor}}
+    // expected-note@-2 {{in instantiation of default function argument}}
+    // expected-note@#B {{declared private}}
+  }
+};
+
+int i = f<B>();
+
+}