diff --git a/history.txt b/history.txt
index 2d7e53ed..819dcf03 100755
--- a/history.txt
+++ b/history.txt
@@ -2347,3 +2347,4 @@ ______
 * Threads: Fixed #318
 * Objects: Fixed #416
 * Objects: Fixed #372
+* Threads: Fixed #644
diff --git a/threads.js b/threads.js
index d5040c58..574fd353 100644
--- a/threads.js
+++ b/threads.js
@@ -1307,7 +1307,7 @@ Process.prototype.doInsertInList = function (element, index, list) {
         return null;
     }
     if (this.inputOption(index) === 'any') {
-        idx = this.reportRandom(1, list.length());
+        idx = this.reportRandom(1, list.length() + 1);
     }
     if (this.inputOption(index) === 'last') {
         idx = list.length() + 1;