diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index cf488850d3752..90cc3f582b641 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -2947,6 +2947,7 @@ bool Expr::isConstantInitializer(ASTContext &Ctx, bool IsForRef,
   }
   case InitListExprClass: {
     const InitListExpr *ILE = cast<InitListExpr>(this);
+    assert(ILE->isSemanticForm() && "InitListExpr must be in semantic form");
     if (ILE->getType()->isArrayType()) {
       unsigned numInits = ILE->getNumInits();
       for (unsigned i = 0; i < numInits; i++) {