diff --git a/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs b/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs
index fa4c09401..ecc937554 100644
--- a/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs
+++ b/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs
@@ -1579,7 +1579,7 @@ private void AddUpdate(ZipUpdate update)
 		{
 			contentsEdited_ = true;
 
-			int index = FindExistingUpdate(update.Entry.Name);
+			int index = FindExistingUpdate(update.Entry);
 
 			if (index >= 0)
 			{
@@ -2489,7 +2489,9 @@ private int FindExistingUpdate(string fileName)
 		{
 			int result = -1;
 
-			string convertedName = GetTransformedFileName(fileName);
+			string convertedName = IsDirectoryName(fileName)
+				? GetTransformedDirectoryName(fileName)
+				: GetTransformedFileName(fileName);
 
 			if (updateIndex_.ContainsKey(convertedName))
 			{
@@ -2511,6 +2513,15 @@ private int FindExistingUpdate(string fileName)
 			return result;
 		}
 
+		private bool IsDirectoryName(string name)
+		{
+			int nameLength = name.Length;
+			bool result =
+				((nameLength > 0) &&
+				((name[nameLength - 1] == '/') || (name[nameLength - 1] == '\\')));
+			return result;
+		}
+
 		/// <summary>
 		/// Get an output stream for the specified <see cref="ZipEntry"/>
 		/// </summary>