diff --git a/ImageFunctions/Thumbnail.cs b/ImageFunctions/Thumbnail.cs
index 1623143..c69ba71 100644
--- a/ImageFunctions/Thumbnail.cs
+++ b/ImageFunctions/Thumbnail.cs
@@ -48,7 +48,7 @@ private static IImageEncoder GetEncoder(string extension)
 
             if (isSupported)
             {
-                switch (extension)
+                switch (extension.ToLower())
                 {
                     case "png":
                         encoder = new PngEncoder();