diff --git a/src/ImageSharp.Formats.Bmp/BmpEncoderCore.cs b/src/ImageSharp.Formats.Bmp/BmpEncoderCore.cs
index 9696eb66d..df62fb6f4 100644
--- a/src/ImageSharp.Formats.Bmp/BmpEncoderCore.cs
+++ b/src/ImageSharp.Formats.Bmp/BmpEncoderCore.cs
@@ -18,7 +18,7 @@ namespace ImageSharp.Formats
         /// <summary>
         /// The options for the encoder.
         /// </summary>
-        private IBmpEncoderOptions options;
+        private readonly IBmpEncoderOptions options;
 
         /// <summary>
         /// The amount to pad each row by.