2 files changed, 10 insertions, 1 deletions
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 56cf5d4fd37..cc2a11fccfb 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -14394,7 +14394,12 @@ Sema::ConditionResult Sema::ActOnCondition(Scope *S, SourceLocation Loc,
   if (Cond.isInvalid())
     return ConditionError();
 
-  return ConditionResult(*this, nullptr, MakeFullExpr(Cond.get(), Loc),
+  // FIXME: FullExprArg doesn't have an invalid bit, so check nullness instead.
+  FullExprArg FullExpr = MakeFullExpr(Cond.get(), Loc);
+  if (!FullExpr.get())
+    return ConditionError();
+
+  return ConditionResult(*this, nullptr, FullExpr,
                          CK == ConditionKind::ConstexprIf);
 }
 
diff --git a/clang/test/SemaCXX/condition.cpp b/clang/test/SemaCXX/condition.cpp
index b757fcb8cd5..5596564d248 100644
--- a/clang/test/SemaCXX/condition.cpp
+++ b/clang/test/SemaCXX/condition.cpp
@@ -65,3 +65,7 @@ void test5() {
 void test5_inst() {
    test5<int>();
 }
+
+void PR28373() {
+  if (!x) {} // expected-error {{undeclared}}
+}