diff --git a/src/main/java/org/apache/ibatis/executor/resultset/DefaultResultSetHandler.java b/src/main/java/org/apache/ibatis/executor/resultset/DefaultResultSetHandler.java
index c1b67f1cec3..68ceb4d6bee 100644
--- a/src/main/java/org/apache/ibatis/executor/resultset/DefaultResultSetHandler.java
+++ b/src/main/java/org/apache/ibatis/executor/resultset/DefaultResultSetHandler.java
@@ -480,7 +480,7 @@ private boolean shouldApplyAutomaticMappings(ResultMap resultMap, boolean isNest
 
   private boolean applyPropertyMappings(ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject,
       ResultLoaderMap lazyLoader, String columnPrefix) throws SQLException {
-    final List<String> mappedColumnNames = rsw.getMappedColumnNames(resultMap, columnPrefix);
+    final Set<String> mappedColumnNames = rsw.getMappedColumnNames(resultMap, columnPrefix);
     boolean foundValues = false;
     final List<ResultMapping> propertyMappings = resultMap.getPropertyResultMappings();
     for (ResultMapping propertyMapping : propertyMappings) {
@@ -1174,7 +1174,7 @@ private void createRowKeyForMappedProperties(ResultMap resultMap, ResultSetWrapp
       if (resultMapping.isSimple()) {
         final String column = prependPrefix(resultMapping.getColumn(), columnPrefix);
         final TypeHandler<?> th = resultMapping.getTypeHandler();
-        List<String> mappedColumnNames = rsw.getMappedColumnNames(resultMap, columnPrefix);
+        Set<String> mappedColumnNames = rsw.getMappedColumnNames(resultMap, columnPrefix);
         // Issue #114
         if (column != null && mappedColumnNames.contains(column.toUpperCase(Locale.ENGLISH))) {
           final Object value = th.getResult(rsw.getResultSet(), column);
diff --git a/src/main/java/org/apache/ibatis/executor/resultset/ResultSetWrapper.java b/src/main/java/org/apache/ibatis/executor/resultset/ResultSetWrapper.java
index ae826baa44a..40ac1a5f247 100644
--- a/src/main/java/org/apache/ibatis/executor/resultset/ResultSetWrapper.java
+++ b/src/main/java/org/apache/ibatis/executor/resultset/ResultSetWrapper.java
@@ -47,7 +47,7 @@ public class ResultSetWrapper {
   private final List<String> classNames = new ArrayList<>();
   private final List<JdbcType> jdbcTypes = new ArrayList<>();
   private final Map<String, Map<Class<?>, TypeHandler<?>>> typeHandlerMap = new HashMap<>();
-  private final Map<String, List<String>> mappedColumnNamesMap = new HashMap<>();
+  private final Map<String, Set<String>> mappedColumnNamesMap = new HashMap<>();
   private final Map<String, List<String>> unMappedColumnNamesMap = new HashMap<>();
 
   public ResultSetWrapper(ResultSet rs, Configuration configuration) throws SQLException {
@@ -144,7 +144,7 @@ private Class<?> resolveClass(String className) {
   }
 
   private void loadMappedAndUnmappedColumnNames(ResultMap resultMap, String columnPrefix) throws SQLException {
-    List<String> mappedColumnNames = new ArrayList<>();
+    Set<String> mappedColumnNames = new HashSet<>();
     List<String> unmappedColumnNames = new ArrayList<>();
     final String upperColumnPrefix = columnPrefix == null ? null : columnPrefix.toUpperCase(Locale.ENGLISH);
     final Set<String> mappedColumns = prependPrefixes(resultMap.getMappedColumns(), upperColumnPrefix);
@@ -160,8 +160,8 @@ private void loadMappedAndUnmappedColumnNames(ResultMap resultMap, String column
     unMappedColumnNamesMap.put(getMapKey(resultMap, columnPrefix), unmappedColumnNames);
   }
 
-  public List<String> getMappedColumnNames(ResultMap resultMap, String columnPrefix) throws SQLException {
-    List<String> mappedColumnNames = mappedColumnNamesMap.get(getMapKey(resultMap, columnPrefix));
+  public Set<String> getMappedColumnNames(ResultMap resultMap, String columnPrefix) throws SQLException {
+    Set<String> mappedColumnNames = mappedColumnNamesMap.get(getMapKey(resultMap, columnPrefix));
     if (mappedColumnNames == null) {
       loadMappedAndUnmappedColumnNames(resultMap, columnPrefix);
       mappedColumnNames = mappedColumnNamesMap.get(getMapKey(resultMap, columnPrefix));