diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -16759,6 +16759,9 @@
       TInfo = Context.getTrivialTypeSourceInfo(T, Loc);
     }
   }
+  if (const auto *U = T->getUnqualifiedDesugaredType())
+    if (U->isUndeducedType())
+      D.setInvalidType();
 
   DiagnoseFunctionSpecifiers(D.getDeclSpec());
 
diff --git a/clang/test/AST/ast-dump-undeduced-field.cpp b/clang/test/AST/ast-dump-undeduced-field.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/AST/ast-dump-undeduced-field.cpp
@@ -0,0 +1,15 @@
+// RUN: not %clang_cc1 -triple x86_64-unknown-unknown -fsyntax-only -ast-dump %s | FileCheck %s
+
+template< class T >
+struct Foo {
+  typedef T type;
+};
+
+struct Bar {
+  Bar();
+  static constexpr auto A = ;
+  Foo<decltype(A)>::type baz;
+};
+
+// CHECK: -CXXRecordDecl {{.*}} invalid struct Bar definition
+// CHECK: -FieldDecl {{.*}} invalid baz {{.*}}
diff --git a/clang/test/SemaCXX/cxx11-crashes.cpp b/clang/test/SemaCXX/cxx11-crashes.cpp
--- a/clang/test/SemaCXX/cxx11-crashes.cpp
+++ b/clang/test/SemaCXX/cxx11-crashes.cpp
@@ -104,3 +104,20 @@
   bool baz() { return __has_nothrow_constructor(B); }
   bool qux() { return __has_nothrow_copy(B); }
 }
+
+namespace undeduced_field {
+template<class T>
+struct Foo {
+  typedef T type;
+};
+
+struct Bar {
+  Bar();
+  // The missing expression makes A undeduced.
+  static constexpr auto A = ;  // expected-error {{expected expression}}
+  Foo<decltype(A)>::type B;  // The type of B is also undeduced (wrapped in Elaborated).
+};
+
+// This used to crash when trying to get the layout of B.
+Bar x;
+}