diff --git a/Elwig/Documents/Pdf.cs b/Elwig/Documents/Pdf.cs
index c024be2..35d9885 100644
--- a/Elwig/Documents/Pdf.cs
+++ b/Elwig/Documents/Pdf.cs
@@ -50,7 +50,7 @@ namespace Elwig.Documents {
             });
         }
 
-        private static void OnConsole(object sender, ConsoleEventArgs e) {
+        private static void OnConsole(object? sender, ConsoleEventArgs e) {
             MessageBox.Show(e.Message.Text);
         }