diff --git a/src/DotTiled.Tests/Serialization/TestData.cs b/src/DotTiled.Tests/Serialization/TestData.cs
index 3e58e6d..582bd70 100644
--- a/src/DotTiled.Tests/Serialization/TestData.cs
+++ b/src/DotTiled.Tests/Serialization/TestData.cs
@@ -42,5 +42,6 @@ public static partial class TestData
     ["Serialization/TestData/Map/map_with_many_layers/map-with-many-layers", (string f) => MapWithManyLayers(f), Array.Empty<ICustomTypeDefinition>()],
     ["Serialization/TestData/Map/map_with_deep_props/map-with-deep-props", (string f) => MapWithDeepProps(), MapWithDeepPropsCustomTypeDefinitions()],
     ["Serialization/TestData/Map/map_with_class/map-with-class", (string f) => MapWithClass(), MapWithClassCustomTypeDefinitions()],
+    ["Serialization/TestData/Map/map_with_class_and_props/map-with-class-and-props", (string f) => MapWithClassAndProps(), MapWithClassAndPropsCustomTypeDefinitions()],
   ];
 }
diff --git a/src/DotTiled.Tests/Serialization/TestData/Map/map-with-class-and-props/map-with-class-and-props.cs b/src/DotTiled.Tests/Serialization/TestData/Map/map-with-class-and-props/map-with-class-and-props.cs
new file mode 100644
index 0000000..8cbd6bd
--- /dev/null
+++ b/src/DotTiled.Tests/Serialization/TestData/Map/map-with-class-and-props/map-with-class-and-props.cs
@@ -0,0 +1,83 @@
+namespace DotTiled.Tests;
+
+public partial class TestData
+{
+  public static Map MapWithClassAndProps() => new Map
+  {
+    Class = "TestClass",
+    Orientation = MapOrientation.Orthogonal,
+    Width = 5,
+    Height = 5,
+    TileWidth = 32,
+    TileHeight = 32,
+    Infinite = false,
+    ParallaxOriginX = 0,
+    ParallaxOriginY = 0,
+    RenderOrder = RenderOrder.RightDown,
+    CompressionLevel = -1,
+    BackgroundColor = new Color { R = 0, G = 0, B = 0, A = 0 },
+    Version = "1.10",
+    TiledVersion = "1.11.0",
+    NextLayerID = 2,
+    NextObjectID = 1,
+    Layers = [
+      new TileLayer
+      {
+        ID = 1,
+        Name = "Tile Layer 1",
+        Width = 5,
+        Height = 5,
+        Data = new Data
+        {
+          Encoding = DataEncoding.Csv,
+          GlobalTileIDs = new Optional<uint[]>([
+            0, 0, 0, 0, 0,
+            0, 0, 0, 0, 0,
+            0, 0, 0, 0, 0,
+            0, 0, 0, 0, 0,
+            0, 0, 0, 0, 0
+          ]),
+          FlippingFlags = new Optional<FlippingFlags[]>([
+            FlippingFlags.None, FlippingFlags.None, FlippingFlags.None, FlippingFlags.None, FlippingFlags.None,
+            FlippingFlags.None, FlippingFlags.None, FlippingFlags.None, FlippingFlags.None, FlippingFlags.None,
+            FlippingFlags.None, FlippingFlags.None, FlippingFlags.None, FlippingFlags.None, FlippingFlags.None,
+            FlippingFlags.None, FlippingFlags.None, FlippingFlags.None, FlippingFlags.None, FlippingFlags.None,
+            FlippingFlags.None, FlippingFlags.None, FlippingFlags.None, FlippingFlags.None, FlippingFlags.None
+          ])
+        }
+      }
+    ],
+    Properties = [
+      new BoolProperty
+      {
+        Name = "classbool",
+        Value = true
+      },
+      new StringProperty
+      {
+        Name = "classstring",
+        Value = "I am not default value"
+      }
+    ]
+  };
+
+  public static IReadOnlyCollection<ICustomTypeDefinition> MapWithClassAndPropsCustomTypeDefinitions() => [
+    new CustomClassDefinition
+    {
+      Name = "TestClass",
+      UseAs = CustomClassUseAs.Map,
+      Members = [
+        new BoolProperty
+        {
+          Name = "classbool",
+          Value = true
+        },
+        new StringProperty
+        {
+          Name = "classstring",
+          Value = "Hello there default value"
+        }
+      ]
+    },
+  ];
+}
diff --git a/src/DotTiled.Tests/Serialization/TestData/Map/map-with-class-and-props/map-with-class-and-props.tmj b/src/DotTiled.Tests/Serialization/TestData/Map/map-with-class-and-props/map-with-class-and-props.tmj
new file mode 100644
index 0000000..d60afe3
--- /dev/null
+++ b/src/DotTiled.Tests/Serialization/TestData/Map/map-with-class-and-props/map-with-class-and-props.tmj
@@ -0,0 +1,39 @@
+{ "class":"TestClass",
+ "compressionlevel":-1,
+ "height":5,
+ "infinite":false,
+ "layers":[
+        {
+         "data":[0, 0, 0, 0, 0,
+            0, 0, 0, 0, 0,
+            0, 0, 0, 0, 0,
+            0, 0, 0, 0, 0,
+            0, 0, 0, 0, 0],
+         "height":5,
+         "id":1,
+         "name":"Tile Layer 1",
+         "opacity":1,
+         "type":"tilelayer",
+         "visible":true,
+         "width":5,
+         "x":0,
+         "y":0
+        }],
+ "nextlayerid":2,
+ "nextobjectid":1,
+ "orientation":"orthogonal",
+ "properties":[
+        {
+         "name":"classstring",
+         "type":"string",
+         "value":"I am not default value"
+        }],
+ "renderorder":"right-down",
+ "tiledversion":"1.11.0",
+ "tileheight":32,
+ "tilesets":[],
+ "tilewidth":32,
+ "type":"map",
+ "version":"1.10",
+ "width":5
+}
\ No newline at end of file
diff --git a/src/DotTiled.Tests/Serialization/TestData/Map/map-with-class/map-with-class.cs b/src/DotTiled.Tests/Serialization/TestData/Map/map-with-class/map-with-class.cs
index 80d50a5..ef98d02 100644
--- a/src/DotTiled.Tests/Serialization/TestData/Map/map-with-class/map-with-class.cs
+++ b/src/DotTiled.Tests/Serialization/TestData/Map/map-with-class/map-with-class.cs
@@ -55,7 +55,7 @@ public partial class TestData
       },
       new StringProperty
       {
-        Name = "stringbool",
+        Name = "classstring",
         Value = "Hello there default value"
       }
     ]
@@ -74,7 +74,7 @@ public partial class TestData
         },
         new StringProperty
         {
-          Name = "stringbool",
+          Name = "classstring",
           Value = "Hello there default value"
         }
       ]
diff --git a/src/DotTiled/Serialization/Tmj/TmjReaderBase.Map.cs b/src/DotTiled/Serialization/Tmj/TmjReaderBase.Map.cs
index 8779dde..caecb7e 100644
--- a/src/DotTiled/Serialization/Tmj/TmjReaderBase.Map.cs
+++ b/src/DotTiled/Serialization/Tmj/TmjReaderBase.Map.cs
@@ -1,6 +1,5 @@
 using System.Collections.Generic;
 using System.Globalization;
-using System.Linq;
 using System.Text.Json;
 
 namespace DotTiled.Serialization.Tmj;
@@ -53,8 +52,7 @@ public abstract partial class TmjReaderBase
     var nextObjectID = element.GetRequiredProperty<uint>("nextobjectid");
     var infinite = element.GetOptionalProperty<bool>("infinite").GetValueOr(false);
 
-    var classProps = Helpers.ResolveClassProperties(@class, _customTypeResolver);
-    var properties = Helpers.MergeProperties(element.GetOptionalPropertyCustom("properties", ReadProperties).GetValueOr([]), classProps).ToList();
+    var properties = ResolveAndMergeProperties(@class, element.GetOptionalPropertyCustom("properties", ReadProperties).GetValueOr([]));
 
     List<BaseLayer> layers = element.GetOptionalPropertyCustom<List<BaseLayer>>("layers", e => e.GetValueAsList<BaseLayer>(el => ReadLayer(el))).GetValueOr([]);
     List<Tileset> tilesets = element.GetOptionalPropertyCustom<List<Tileset>>("tilesets", e => e.GetValueAsList<Tileset>(el => ReadTileset(el, version, tiledVersion))).GetValueOr([]);
diff --git a/src/DotTiled/Serialization/Tmj/TmjReaderBase.cs b/src/DotTiled/Serialization/Tmj/TmjReaderBase.cs
index f36ca88..f32100a 100644
--- a/src/DotTiled/Serialization/Tmj/TmjReaderBase.cs
+++ b/src/DotTiled/Serialization/Tmj/TmjReaderBase.cs
@@ -1,4 +1,6 @@
 using System;
+using System.Collections.Generic;
+using System.Linq;
 using System.Text.Json;
 
 namespace DotTiled.Serialization.Tmj;
@@ -40,6 +42,12 @@ public abstract partial class TmjReaderBase : IDisposable
     _customTypeResolver = customTypeResolver ?? throw new ArgumentNullException(nameof(customTypeResolver));
   }
 
+  private List<IProperty> ResolveAndMergeProperties(string className, List<IProperty> readProperties)
+  {
+    var classProps = Helpers.ResolveClassProperties(className, _customTypeResolver);
+    return Helpers.MergeProperties(classProps, readProperties).ToList();
+  }
+
   /// <inheritdoc/>
   protected virtual void Dispose(bool disposing)
   {
diff --git a/src/DotTiled/Serialization/Tmx/TmxReaderBase.Map.cs b/src/DotTiled/Serialization/Tmx/TmxReaderBase.Map.cs
index a16b715..ed3a492 100644
--- a/src/DotTiled/Serialization/Tmx/TmxReaderBase.Map.cs
+++ b/src/DotTiled/Serialization/Tmx/TmxReaderBase.Map.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Globalization;
+using System.Linq;
 
 namespace DotTiled.Serialization.Tmx;
 
@@ -56,6 +57,7 @@ public abstract partial class TmxReaderBase
     var infinite = _reader.GetOptionalAttributeParseable<uint>("infinite").GetValueOr(0) == 1;
 
     // At most one of
+    var propertiesCounter = 0;
     List<IProperty> properties = Helpers.ResolveClassProperties(@class, _customTypeResolver);
 
     // Any number of
@@ -64,7 +66,7 @@ public abstract partial class TmxReaderBase
 
     _reader.ProcessChildren("map", (r, elementName) => elementName switch
     {
-      "properties" => () => Helpers.SetAtMostOnce(ref properties, ReadProperties(), "Properties"),
+      "properties" => () => Helpers.SetAtMostOnceUsingCounter(ref properties, Helpers.MergeProperties(properties, ReadProperties()).ToList(), "Properties", ref propertiesCounter),
       "tileset" => () => tilesets.Add(ReadTileset(version, tiledVersion)),
       "layer" => () => layers.Add(ReadTileLayer(infinite)),
       "objectgroup" => () => layers.Add(ReadObjectLayer()),