diff --git a/ImageFunctions/Thumbnail.cs b/ImageFunctions/Thumbnail.cs
index 7a0574d..f176da3 100644
--- a/ImageFunctions/Thumbnail.cs
+++ b/ImageFunctions/Thumbnail.cs
@@ -43,7 +43,7 @@ private static IImageEncoder GetEncoder(string extension)
         {
             IImageEncoder encoder = null;
 
-            extension = extension.Replace(".", "");
+            extension = extension.Replace(".", "").ToLower();
 
             var isSupported = Regex.IsMatch(extension, "gif|png|jpe?g", RegexOptions.IgnoreCase);