diff --git a/src/ICSharpCode.SharpZipLib/GZip/GzipOutputStream.cs b/src/ICSharpCode.SharpZipLib/GZip/GzipOutputStream.cs
index 31985f93..0b1a647f 100644
--- a/src/ICSharpCode.SharpZipLib/GZip/GzipOutputStream.cs
+++ b/src/ICSharpCode.SharpZipLib/GZip/GzipOutputStream.cs
@@ -243,7 +243,7 @@ public override void Finish()
 
 		#region Support Routines
 
-		private string CleanFilename(string path)
+		private static string CleanFilename(string path)
 			=> path.Substring(path.LastIndexOf('/') + 1);
 
 		private void WriteHeader()
diff --git a/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs b/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs
index a99f1f5b..3bd66ffe 100644
--- a/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs
+++ b/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs
@@ -2485,7 +2485,7 @@ private void CopyDescriptorBytes(ZipUpdate update, Stream dest, Stream source)
 		/// <param name="update">The update to get the size for.</param>
 		/// <param name="includingSignature">Whether to include the signature size</param>
 		/// <returns>The descriptor size, zero if there isn't one.</returns>
-		private int GetDescriptorSize(ZipUpdate update, bool includingSignature)
+		private static int GetDescriptorSize(ZipUpdate update, bool includingSignature)
 		{
 			if (!((GeneralBitFlags)update.Entry.Flags).HasFlag(GeneralBitFlags.Descriptor)) 
 				return 0;