diff --git a/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs b/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs
index c12a53df1..056785e16 100644
--- a/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs
+++ b/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs
@@ -1626,7 +1626,7 @@ private void AddUpdate(ZipUpdate update)
 		{
 			contentsEdited_ = true;
 
-			int index = FindExistingUpdate(update.Entry.Name);
+			int index = FindExistingUpdate(update.Entry.Name, isEntryName: true);
 
 			if (index >= 0)
 			{
@@ -2555,13 +2555,9 @@ private void CopyEntryDataDirect(ZipUpdate update, Stream stream, bool updateCrc
 		private int FindExistingUpdate(ZipEntry entry)
 		{
 			int result = -1;
-			string convertedName = entry.IsDirectory
-				? GetTransformedDirectoryName(entry.Name)
-				: GetTransformedFileName(entry.Name);
-
-			if (updateIndex_.ContainsKey(convertedName))
+			if (updateIndex_.ContainsKey(entry.Name))
 			{
-				result = (int)updateIndex_[convertedName];
+				result = (int)updateIndex_[entry.Name];
 			}
 			/*
 						// This is slow like the coming of the next ice age but takes less storage and may be useful
@@ -2579,11 +2575,11 @@ private int FindExistingUpdate(ZipEntry entry)
 			return result;
 		}
 
-		private int FindExistingUpdate(string fileName)
+		private int FindExistingUpdate(string fileName, bool isEntryName = false)
 		{
 			int result = -1;
 
-			string convertedName = GetTransformedFileName(fileName);
+			string convertedName = !isEntryName ? GetTransformedFileName(fileName) : fileName;
 
 			if (updateIndex_.ContainsKey(convertedName))
 			{