diff --git a/core/src/processing/core/PApplet.java b/core/src/processing/core/PApplet.java
index c117e50d0..1aed9048a 100644
--- a/core/src/processing/core/PApplet.java
+++ b/core/src/processing/core/PApplet.java
@@ -6650,7 +6650,7 @@ public class PApplet implements PConstants {
       } else if (opt.startsWith("extension=")) {
         extensions = new String[] { opt.substring(10) };
       } else if (opt.startsWith("extensions=")) {
-        extensions = split(opt.substring(10), ',');
+        extensions = split(opt.substring(11), ',');
       } else if (opt.equals("files")) {
         directories = false;
       } else if (opt.equals("directories")) {
diff --git a/core/todo.txt b/core/todo.txt
index 70bb06738..626f247dc 100644
--- a/core/todo.txt
+++ b/core/todo.txt
@@ -1,4 +1,6 @@
 1273 (4.0a4)
+X fix typo in extensions= arg
+
 
 _ why does japplemenubar.JAppleMenuBar.hide(); still work?
 _   it calls SetSystemUIMode, which is part of Carbon (which was removed in Catalina)