diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -4844,6 +4844,8 @@
 }
 
 static bool EvaluateVarDecl(EvalInfo &Info, const VarDecl *VD) {
+  if (VD->isInvalidDecl())
+    return false;
   // We don't need to evaluate the initializer for a static local.
   if (!VD->hasLocalStorage())
     return true;
diff --git a/clang/test/SemaCXX/constexpr-value-init.cpp b/clang/test/SemaCXX/constexpr-value-init.cpp
--- a/clang/test/SemaCXX/constexpr-value-init.cpp
+++ b/clang/test/SemaCXX/constexpr-value-init.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 %s -Wno-uninitialized -std=c++11 -fsyntax-only -verify
+// RUN: %clang_cc1 %s -Wno-uninitialized -std=c++17 -fsyntax-only -verify
 
 struct A {
   constexpr A() : a(b + 1), b(a + 1) {} // expected-note 5{{outside its lifetime}}
@@ -46,3 +46,17 @@
 static_assert(e2.a[0].b == 2, "");
 static_assert(e2.a[1].a == 1, "");
 static_assert(e2.a[1].b == 2, "");
+
+namespace InvalidDeclInsideConstExpr {
+template <int a> struct i; // expected-note {{template is declared here}}
+template <> struct i<0> {};
+
+template <int x> constexpr auto c() {
+  // i<x> is valid, but it might be incomplete. g would be invalid in that case.
+  i<x> g; // expected-error {{implicit instantiation of undefined template 'InvalidDeclInsideConstExpr::i<1>'}}
+  return 0;
+}
+
+auto y = c<1>(); // expected-note {{in instantiation of function template specialization 'InvalidDeclInsideConstExpr::c<1>' requested here}}
+auto x = c<0>(); // this is valid.
+}