diff --git a/HISTORY.md b/HISTORY.md
index a400e404..372e1df3 100755
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -37,6 +37,7 @@
     * fixed copying unattached comments among sprites, thanks, Jadga, for the report!
     * disabled dropping reporters onto message hat block input slots
     * fixed outdated blocks specs for "When I am ..." hat block in many translations
+    * fixed duplicating custom block definitions that don't have a body
 * **Documentation Updates:**
     * updated manual, thanks Brian!
     * updated readme, thanks, Michael!
@@ -44,6 +45,9 @@
     * German
     * Chinese, thanks, Simon!
 
+### 2021-10-25
+* byob: fixed #2902
+
 ### 2021-10-22
 * blocks, objects: only show the "message" upvar in the "When I receive" hat if "any message" is selected
 * blocks: only show "key" upvar in the "When ... is pressed" hat if "any key" is selected
diff --git a/snap.html b/snap.html
index 362eda1d..1804f0ad 100755
--- a/snap.html
+++ b/snap.html
@@ -23,7 +23,7 @@
         <script src="src/gui.js?version=2021-10-20"></script>
         <script src="src/paint.js?version=2021-07-05"></script>
         <script src="src/lists.js?version=2021-07-19"></script>
-        <script src="src/byob.js?version=2021-10-14"></script>
+        <script src="src/byob.js?version=2021-10-25"></script>
         <script src="src/tables.js?version=2021-05-07"></script>
         <script src="src/sketch.js?version=2021-07-05"></script>
         <script src="src/video.js?version=2019-06-27"></script>
diff --git a/src/byob.js b/src/byob.js
index 296ddb91..6d9897ff 100644
--- a/src/byob.js
+++ b/src/byob.js
@@ -108,7 +108,7 @@ WatcherMorph, XML_Serializer, SnapTranslator, SnapExtensions*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.byob = '2021-October-14';
+modules.byob = '2021-October-25';
 
 // Declarations
 
@@ -1287,7 +1287,7 @@ CustomCommandBlockMorph.prototype.duplicateBlockDefinition = function () {
         def = this.isGlobal ? this.definition : rcvr.getMethod(this.blockSpec),
         dup = def.copyAndBindTo(rcvr),
         spec = dup.spec,
-        exp = dup.body.expression,
+        exp = dup.body? dup.body.expression : null,
         count = 1;
 
     function rebindRecursiveCalls(topBlock) {