diff --git a/src/map.cpp b/src/map.cpp
index 3a6a299..9ab40c2 100644
--- a/src/map.cpp
+++ b/src/map.cpp
@@ -17,7 +17,7 @@ namespace YAML
 		for(node_map::const_iterator it=data.begin();it!=data.end();++it) {
 			std::auto_ptr<Node> pKey = it->first->Clone();
 			std::auto_ptr<Node> pValue = it->second->Clone();
-			m_data[pKey.release()] = pValue.release();
+			AddEntry(pKey, pValue);
 		}
 	}
 
@@ -104,8 +104,7 @@ namespace YAML
 				pValue->Parse(pScanner, state);
 			}
 
-			// assign the map with the actual pointers
-			m_data[pKey.release()] = pValue.release();
+			AddEntry(pKey, pValue);
 		}
 
 		state.PopCollectionType(ParserState::BLOCK_MAP);
@@ -149,8 +148,7 @@ namespace YAML
 			else if(nextToken.type != Token::FLOW_MAP_END)
 				throw ParserException(nextToken.mark, ErrorMsg::END_OF_MAP_FLOW);
 
-			// assign the map with the actual pointers
-			m_data[pKey.release()] = pValue.release();
+			AddEntry(pKey, pValue);
 		}
 
 		state.PopCollectionType(ParserState::FLOW_MAP);
@@ -173,8 +171,7 @@ namespace YAML
 			pValue->Parse(pScanner, state);
 		}
 			
-		// assign the map with the actual pointers
-		m_data[pKey.release()] = pValue.release();
+		AddEntry(pKey, pValue);
 		state.PopCollectionType(ParserState::COMPACT_MAP);
 	}
 	
@@ -188,12 +185,20 @@ namespace YAML
 		// grab value
 		pScanner->pop();
 		pValue->Parse(pScanner, state);
-			
-		// assign the map with the actual pointers
-		m_data[pKey.release()] = pValue.release();
+
+		AddEntry(pKey, pValue);
 		state.PopCollectionType(ParserState::COMPACT_MAP);
 	}
 	
+	void Map::AddEntry(std::auto_ptr<Node> pKey, std::auto_ptr<Node> pValue)
+	{
+		node_map::const_iterator it = m_data.find(pKey.get());
+		if(it != m_data.end())
+			return;
+		
+		m_data[pKey.release()] = pValue.release();
+	}
+
 	void Map::Write(Emitter& out) const
 	{
 		out << BeginMap;
diff --git a/src/map.h b/src/map.h
index bb8f949..bcfae4b 100644
--- a/src/map.h
+++ b/src/map.h
@@ -43,6 +43,8 @@ namespace YAML
 		void ParseFlow(Scanner *pScanner, ParserState& state);
 		void ParseCompact(Scanner *pScanner, ParserState& state);
 		void ParseCompactWithNoKey(Scanner *pScanner, ParserState& state);
+		
+		void AddEntry(std::auto_ptr<Node> pKey, std::auto_ptr<Node> pValue);
 
 	private:
 		node_map m_data;