diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -7084,7 +7084,8 @@
   //   functions. In such a case, the candidate functions generated from each
   //   function template are combined with the set of non-template candidate
   //   functions.
-  TemplateDeductionInfo Info(CandidateSet.getLocation());
+  TemplateDeductionInfo Info(CandidateSet.getLocation(),
+                             MethodTmpl->getTemplateParameters()->getDepth());
   FunctionDecl *Specialization = nullptr;
   ConversionSequenceList Conversions;
   if (TemplateDeductionResult Result = DeduceTemplateArguments(
@@ -14171,8 +14172,12 @@
       IsError |= InputInit.isInvalid();
       Arg = InputInit.getAs<Expr>();
     } else {
-      ExprResult DefArg =
-          S.BuildCXXDefaultArgExpr(LParenLoc, Method, Method->getParamDecl(i));
+      ParmVarDecl *Param = Method->getParamDecl(i);
+      if (!Param->hasDefaultArg()) {
+        IsError = true;
+        break;
+      }
+      ExprResult DefArg = S.BuildCXXDefaultArgExpr(LParenLoc, Method, Param);
       if (DefArg.isInvalid()) {
         IsError = true;
         break;
diff --git a/clang/test/CXX/temp/temp.decls/temp.variadic/p5-cxx20.cpp b/clang/test/CXX/temp/temp.decls/temp.variadic/p5-cxx20.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/CXX/temp/temp.decls/temp.variadic/p5-cxx20.cpp
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %s
+// expected-no-diagnostics
+
+namespace pr28087 {
+template <typename F> auto apply(F f) { f(); }
+template <class...> struct S {
+  template <int> auto f(decltype(apply([](auto...) {})));
+};
+template struct S<>;
+} // namespace pr28087