diff --git a/src/emitter.cpp b/src/emitter.cpp
index 644b312..4d48307 100644
--- a/src/emitter.cpp
+++ b/src/emitter.cpp
@@ -533,7 +533,8 @@ void Emitter::BlockMapPrepareNode(EmitterNodeType::value child) {
     if (m_pState->GetMapKeyFormat() == LongKey)
       m_pState->SetLongKey();
     if (child == EmitterNodeType::BlockSeq ||
-        child == EmitterNodeType::BlockMap)
+        child == EmitterNodeType::BlockMap ||
+        child == EmitterNodeType::Property)
       m_pState->SetLongKey();
 
     if (m_pState->CurGroupLongKey())