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
@@ -6229,6 +6229,8 @@
     return false;
 
   const CXXRecordDecl *RD = Definition->getParent();
+  assert(RD->hasDefinition() && "Definition is needed to read the fields");
+  RD = RD->getDefinition();
   if (RD->getNumVBases()) {
     Info.FFDiag(CallLoc, diag::note_constexpr_virtual_base) << RD;
     return false;