Index: llvm/lib/Demangle/MicrosoftDemangle.cpp
===================================================================
--- llvm/lib/Demangle/MicrosoftDemangle.cpp
+++ llvm/lib/Demangle/MicrosoftDemangle.cpp
@@ -1389,9 +1389,12 @@
     return nullptr;
 
   if (Identifier->kind() == NodeKind::StructorIdentifier) {
+    if (QN->Components->Count < 2) {
+      Error = true;
+      return nullptr;
+    }
     StructorIdentifierNode *SIN =
         static_cast<StructorIdentifierNode *>(Identifier);
-    assert(QN->Components->Count >= 2);
     Node *ClassNode = QN->Components->Nodes[QN->Components->Count - 2];
     SIN->Class = static_cast<IdentifierNode *>(ClassNode);
   }
Index: llvm/test/Demangle/invalid-manglings.test
===================================================================
--- llvm/test/Demangle/invalid-manglings.test
+++ llvm/test/Demangle/invalid-manglings.test
@@ -19,3 +19,8 @@
 ; CHECK-EMPTY:
 ; CHECK-NEXT: ??
 ; CHECK-NEXT: error: Invalid mangled name
+
+??0@
+; CHECK-EMPTY:
+; CHECK-NEXT: ??0@
+; CHECK-NEXT: error: Invalid mangled name