diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 4ae5ab42ff79..5420876866d3 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -538,8 +538,10 @@ namespace {
                                  = diag::note_invalid_subexpr_in_const_expr,
                                unsigned ExtraNotes = 0) {
       // Don't override a previous diagnostic.
-      if (!EvalStatus.Diag || !EvalStatus.Diag->empty())
+      if (!EvalStatus.Diag || !EvalStatus.Diag->empty()) {
+        HasActiveDiagnostic = false;
         return OptionalDiagnostic();
+      }
       return Diag(Loc, DiagId, ExtraNotes);
     }
 
diff --git a/clang/test/Sema/const-eval.c b/clang/test/Sema/const-eval.c
index 22ac67adad99..a9c8806b5d99 100644
--- a/clang/test/Sema/const-eval.c
+++ b/clang/test/Sema/const-eval.c
@@ -112,3 +112,8 @@ int castViaInt[*(int*)(unsigned long)"test"]; // expected-error {{variable lengt
 // PR11391.
 struct PR11391 { _Complex float f; } pr11391;
 EVAL_EXPR(42, __builtin_constant_p(pr11391.f = 1))
+
+// PR12043
+float varfloat;
+const float constfloat = 0;
+EVAL_EXPR(43, varfloat && constfloat) // expected-error {{must have a constant size}}