diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -2929,8 +2929,8 @@
   // Recovery AST still heavily relies on dependent-type machinery.
   Opts.RecoveryAST =
       Args.hasFlag(OPT_frecovery_ast, OPT_fno_recovery_ast, Opts.CPlusPlus);
-  Opts.RecoveryASTType =
-      Args.hasFlag(OPT_frecovery_ast_type, OPT_fno_recovery_ast_type, false);
+  Opts.RecoveryASTType = Args.hasFlag(
+      OPT_frecovery_ast_type, OPT_fno_recovery_ast_type, Opts.CPlusPlus);
   Opts.HeinousExtensions = Args.hasArg(OPT_fheinous_gnu_extensions);
   Opts.AccessControl = !Args.hasArg(OPT_fno_access_control);
   Opts.ElideConstructors = !Args.hasArg(OPT_fno_elide_constructors);
diff --git a/clang/test/CXX/temp/temp.constr/temp.constr.order/function-templates.cpp b/clang/test/CXX/temp/temp.constr/temp.constr.order/function-templates.cpp
--- a/clang/test/CXX/temp/temp.constr/temp.constr.order/function-templates.cpp
+++ b/clang/test/CXX/temp/temp.constr/temp.constr.order/function-templates.cpp
@@ -67,7 +67,8 @@
 // expected-note@-1 {{candidate function [with T = long long, U = int]}}
 
 static_assert(sizeof(f<long long, int>()));
-// expected-error@-1 {{call to 'f' is ambiguous}}
+// expected-error@-1 {{call to 'f' is ambiguous}} \
+   expected-error@-1 {{invalid application of 'sizeof' to an incomplete type 'void'}}
 
 template<typename T>
 concept C3 = true;
diff --git a/clang/test/CXX/temp/temp.decls/temp.variadic/fixed-expansion.cpp b/clang/test/CXX/temp/temp.decls/temp.variadic/fixed-expansion.cpp
--- a/clang/test/CXX/temp/temp.decls/temp.variadic/fixed-expansion.cpp
+++ b/clang/test/CXX/temp/temp.decls/temp.variadic/fixed-expansion.cpp
@@ -123,7 +123,10 @@
   template<typename,typename,typename> struct S {};
   template<typename T, typename U> using U = S<T, int, U>; // expected-note 2{{template parameter is declared here}}
   template<typename...Ts> U<Ts...> &f(U<Ts...>, Ts...); // expected-error 2{{pack expansion used as argument for non-pack parameter of alias template}}
-  S<int, int, double> &s1 = f({}, 0, 0.0); // expected-error {{no matching function}}
+  // The return type of f is invalid during instantiation, and int is the fallback.
+  // FIXME: would be nice to suppress the secondard "cannot bind to a value of unrelated type 'int'" diagnostic.
+  S<int, int, double> &s1 = f({}, 0, 0.0); // expected-error {{no matching function}} \
+                                              expected-error {{non-const lvalue reference to type 'S<int, int, double>' cannot bind to a value of unrelated type 'int'}}
 }
 
 namespace PR18401 {
diff --git a/clang/test/SemaTemplate/dependent-names.cpp b/clang/test/SemaTemplate/dependent-names.cpp
--- a/clang/test/SemaTemplate/dependent-names.cpp
+++ b/clang/test/SemaTemplate/dependent-names.cpp
@@ -173,7 +173,7 @@
 
 
   namespace O {
-    void f(char&); // expected-note {{candidate function not viable}}
+    int f(char&); // expected-note {{candidate function not viable}}
 
     template<typename T> struct C {
       static const int n = f(T()); // expected-error {{no matching function}}