diff --git a/core/src/processing/data/StringList.java b/core/src/processing/data/StringList.java
index b5ec4bad0..7434c0e77 100644
--- a/core/src/processing/data/StringList.java
+++ b/core/src/processing/data/StringList.java
@@ -309,7 +309,7 @@ public class StringList implements Iterable<String> {
     if (index < 0) {
       throw new IllegalArgumentException("insert() index cannot be negative: it was " + index);
     }
-    if (index >= values.length) {
+    if (index >= data.length) {
       throw new IllegalArgumentException("insert() index " + index + " is past the end of this list");
     }