diff --git a/src/ICSharpCode.SharpZipLib/Zip/ZipEntry.cs b/src/ICSharpCode.SharpZipLib/Zip/ZipEntry.cs
index 3baf8415d..2f326ab0e 100644
--- a/src/ICSharpCode.SharpZipLib/Zip/ZipEntry.cs
+++ b/src/ICSharpCode.SharpZipLib/Zip/ZipEntry.cs
@@ -1125,7 +1125,7 @@ internal void ProcessExtraData(bool localHeader)
 			}
 		}
 
-		private DateTime? GetDateTime(ZipExtraData extraData)
+		private static DateTime? GetDateTime(ZipExtraData extraData)
 		{
 			// Check for NT timestamp
 			// NOTE: Disable by default to match behavior of InfoZIP
diff --git a/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs b/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs
index 62015a932..c908af0f0 100644
--- a/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs
+++ b/src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs
@@ -1904,7 +1904,7 @@ public void AddDirectory(string directoryName)
 		/// Check if the specified compression method is supported for adding a new entry.
 		/// </summary>
 		/// <param name="compressionMethod">The compression method for the new entry.</param>
-		private void CheckSupportedCompressionMethod(CompressionMethod compressionMethod)
+		private static void CheckSupportedCompressionMethod(CompressionMethod compressionMethod)
 		{
 			if (compressionMethod != CompressionMethod.Deflated && compressionMethod != CompressionMethod.Stored && compressionMethod != CompressionMethod.BZip2)
 			{