diff --git a/sources/OpenMcdf.Extensions/OLEProperties/OLEPropertiesContainer.cs b/sources/OpenMcdf.Extensions/OLEProperties/OLEPropertiesContainer.cs
index fd962102..e3b66889 100644
--- a/sources/OpenMcdf.Extensions/OLEProperties/OLEPropertiesContainer.cs
+++ b/sources/OpenMcdf.Extensions/OLEProperties/OLEPropertiesContainer.cs
@@ -154,9 +154,10 @@ internal OLEPropertiesContainer(CFStream cfStream)
                     UserDefinedProperties.properties.Add(op);
                 }
 
-                UserDefinedProperties.PropertyNames = (Dictionary<uint, string>)pStream.PropertySet1.Properties
+                var existingPropertyNames = (Dictionary<uint, string>)pStream.PropertySet1.Properties
                     .Where(p => p.PropertyType == PropertyType.DictionaryProperty).FirstOrDefault()?.Value;
 
+                UserDefinedProperties.PropertyNames = existingPropertyNames ?? new Dictionary<uint, string> ();
             }
         }
 
diff --git a/sources/Test/OpenMcdf.Extensions.Test/OLEPropertiesExtensionsTest.cs b/sources/Test/OpenMcdf.Extensions.Test/OLEPropertiesExtensionsTest.cs
index cb2a5e5b..eaa8b5f8 100644
--- a/sources/Test/OpenMcdf.Extensions.Test/OLEPropertiesExtensionsTest.cs
+++ b/sources/Test/OpenMcdf.Extensions.Test/OLEPropertiesExtensionsTest.cs
@@ -371,5 +371,74 @@ public void Test_Read_Unicode_User_Properties_Dictionary()
                 Assert.AreEqual("XYZ!\0", propArray[5].Value);
             }
         }
+
+        // Test that we can add user properties of various types and then read them back
+        [TestMethod]
+        public void Test_DOCUMENT_SUMMARY_INFO_ADD_CUSTOM()
+        {
+            if (File.Exists("test_add_user_defined_property.doc"))
+                File.Delete("test_add_user_defined_property.doc");
+
+            // Test value for a VT_FILETIME property
+            DateTime testNow = DateTime.Now;
+
+            // english.presets.doc has a user defined property section, but no properties other than the codepage
+            using (CompoundFile cf = new CompoundFile("english.presets.doc"))
+            {
+                var dsiStream = cf.RootStorage.GetStream("\u0005DocumentSummaryInformation");
+                var co = dsiStream.AsOLEPropertiesContainer();
+                var userProperties = co.UserDefinedProperties;
+
+                userProperties.PropertyNames[2] = "StringProperty";
+                userProperties.PropertyNames[3] = "BooleanProperty";
+                userProperties.PropertyNames[4] = "IntegerProperty";
+                userProperties.PropertyNames[5] = "DateProperty";
+
+                var stringProperty = co.NewProperty(VTPropertyType.VT_LPSTR, 2);
+                stringProperty.Value = "Hello";
+                userProperties.AddProperty(stringProperty);
+
+                var booleanProperty = co.NewProperty(VTPropertyType.VT_BOOL, 3);
+                booleanProperty.Value = true;
+                userProperties.AddProperty(booleanProperty);
+
+                var integerProperty = co.NewProperty(VTPropertyType.VT_I4, 4);
+                integerProperty.Value = 3456;
+                userProperties.AddProperty(integerProperty);
+
+                var timeProperty = co.NewProperty(VTPropertyType.VT_FILETIME, 5);
+                timeProperty.Value = testNow;
+                userProperties.AddProperty(timeProperty);
+
+                co.Save(dsiStream);
+                cf.SaveAs(@"test_add_user_defined_property.doc");
+            }
+
+            using (CompoundFile cf = new CompoundFile("test_add_user_defined_property.doc"))
+            {
+                var co = cf.RootStorage.GetStream("\u0005DocumentSummaryInformation").AsOLEPropertiesContainer();
+                var propArray = co.UserDefinedProperties.Properties.ToArray();
+                Assert.AreEqual(propArray.Length, 5);
+
+                // CodePage prop
+                Assert.AreEqual(1u, propArray[0].PropertyIdentifier);
+                Assert.AreEqual("0x00000001", propArray[0].PropertyName);
+                Assert.AreEqual((short)-535, propArray[0].Value);
+
+                // User properties
+                Assert.AreEqual("StringProperty\0", propArray[1].PropertyName);
+                Assert.AreEqual("Hello\0", propArray[1].Value);
+                Assert.AreEqual(VTPropertyType.VT_LPSTR, propArray[1].VTType);
+                Assert.AreEqual("BooleanProperty\0", propArray[2].PropertyName);
+                Assert.AreEqual(true, propArray[2].Value);
+                Assert.AreEqual(VTPropertyType.VT_BOOL, propArray[2].VTType);
+                Assert.AreEqual("IntegerProperty\0", propArray[3].PropertyName);
+                Assert.AreEqual(3456, propArray[3].Value);
+                Assert.AreEqual(VTPropertyType.VT_I4, propArray[3].VTType);
+                Assert.AreEqual("DateProperty\0", propArray[4].PropertyName);
+                Assert.AreEqual(testNow, propArray[4].Value);
+                Assert.AreEqual(VTPropertyType.VT_FILETIME, propArray[4].VTType);
+            }
+        }
     }
 }