diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs b/src/libraries/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs
index b316e88b87e38..b8aa53b73b148 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Serialization/XmlSerializer.cs
@@ -177,7 +177,10 @@ public XmlSerializer(XmlTypeMapping xmlTypeMapping)
             if (xmlTypeMapping == null)
                 throw new ArgumentNullException(nameof(xmlTypeMapping));
 
-            _tempAssembly = GenerateTempAssembly(xmlTypeMapping);
+            if (Mode != SerializationMode.ReflectionOnly)
+            {
+                _tempAssembly = GenerateTempAssembly(xmlTypeMapping);
+            }
             _mapping = xmlTypeMapping;
         }
 
@@ -256,7 +259,10 @@ public XmlSerializer(Type type, XmlAttributeOverrides? overrides, Type[]? extraT
             DefaultNamespace = defaultNamespace;
             _rootType = type;
             _mapping = GenerateXmlTypeMapping(type, overrides, extraTypes, root, defaultNamespace);
-            _tempAssembly = GenerateTempAssembly(_mapping, type, defaultNamespace, location);
+            if (Mode != SerializationMode.ReflectionOnly)
+            {
+                _tempAssembly = GenerateTempAssembly(_mapping, type, defaultNamespace, location);
+            }
         }
 
         private XmlTypeMapping GenerateXmlTypeMapping(Type type, XmlAttributeOverrides? overrides, Type[]? extraTypes, XmlRootAttribute? root, string? defaultNamespace)