diff --git a/history.txt b/history.txt
index 44160ca3..53e6087e 100755
--- a/history.txt
+++ b/history.txt
@@ -2153,3 +2153,4 @@ ______
 140605
 ------
 * Objects: stop replacing the empty string with the number zero in watchers
+* Threads: initialize new variables with zero (instead of null)
diff --git a/threads.js b/threads.js
index 21147a34..d4894412 100644
--- a/threads.js
+++ b/threads.js
@@ -83,7 +83,7 @@ ArgLabelMorph, localize, XML_Element, hex_sha512*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.threads = '2014-May-20';
+modules.threads = '2014-Jun-05';
 
 var ThreadManager;
 var Process;
@@ -3054,7 +3054,7 @@ VariableFrame.prototype.getVar = function (name, upvars) {
 VariableFrame.prototype.addVar = function (name, value) {
     this.vars[name] = (value === 0 ? 0
               : value === false ? false
-                       : value === '' ? '' : value || null);
+                       : value === '' ? '' : value || 0);
 };
 
 VariableFrame.prototype.deleteVar = function (name) {