diff --git a/core/src/main/java/edu/umd/cs/piccolo/event/PInputEventFilter.java b/core/src/main/java/edu/umd/cs/piccolo/event/PInputEventFilter.java
index 0c2dbe5..3e2d96e 100644
--- a/core/src/main/java/edu/umd/cs/piccolo/event/PInputEventFilter.java
+++ b/core/src/main/java/edu/umd/cs/piccolo/event/PInputEventFilter.java
@@ -53,7 +53,7 @@
  */
 public class PInputEventFilter {
 
-    public static int ALL_MODIFIERS_MASK = InputEvent.BUTTON1_MASK | InputEvent.BUTTON2_MASK | InputEvent.BUTTON3_MASK
+    public static final int ALL_MODIFIERS_MASK = InputEvent.BUTTON1_MASK | InputEvent.BUTTON2_MASK | InputEvent.BUTTON3_MASK
             | InputEvent.SHIFT_MASK | InputEvent.CTRL_MASK | InputEvent.ALT_MASK | InputEvent.ALT_GRAPH_MASK
             | InputEvent.META_MASK;