diff --git a/MimeKit/Tnef/TnefPropertyTag.cs b/MimeKit/Tnef/TnefPropertyTag.cs
index 62224cc86c..fed007a6a2 100644
--- a/MimeKit/Tnef/TnefPropertyTag.cs
+++ b/MimeKit/Tnef/TnefPropertyTag.cs
@@ -5460,8 +5460,8 @@ public struct TnefPropertyTag
 		/// </remarks>
 		public static readonly TnefPropertyTag Ypos = new TnefPropertyTag (TnefPropertyId.Ypos, TnefPropertyType.Long);
 
-		//const TnefPropertyId NamedMin = unchecked ((TnefPropertyId) 0x8000);
-		//const TnefPropertyId NamedMax = unchecked ((TnefPropertyId) 0xFFFE);
+		const TnefPropertyId NamedMin = unchecked ((TnefPropertyId) 0x8000);
+		const TnefPropertyId NamedMax = unchecked ((TnefPropertyId) 0xFFFE);
 		const short MultiValuedFlag = (short) TnefPropertyType.MultiValued;
 		readonly TnefPropertyType type;
 		readonly TnefPropertyId id;
@@ -5496,7 +5496,7 @@ public bool IsMultiValued {
 		/// </remarks>
 		/// <value><c>true</c> if the property has a special name; otherwise, <c>false</c>.</value>
 		public bool IsNamed {
-			get { return true; }
+			get { return (int) id >= (int) NamedMin && (int) id <= (int) NamedMax; }
 		}
 
 		/// <summary>