diff --git a/HISTORY.md b/HISTORY.md
index 42e9287b..c5570ee1 100755
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -7,6 +7,9 @@
 * **Notable Fixes:**
     * fixed keyboard formula entry for subtraction
 
+### 2020-12-16
+* threads, objects: added dev debugging hook for counting yields
+
 ### 2020-12-14
 * new dev version
 * objects: fixed keyboard formula entry for subtraction
diff --git a/snap.html b/snap.html
index 33f8c41f..f1596b2d 100755
--- a/snap.html
+++ b/snap.html
@@ -9,8 +9,8 @@
         <script src="src/symbols.js?version=2020-10-07"></script>
         <script src="src/widgets.js?version=2020-10-06"></script>
         <script src="src/blocks.js?version=2020-12-15"></script>
-        <script src="src/threads.js?version=2020-12-09"></script>
-        <script src="src/objects.js?version=2020-12-15"></script>
+        <script src="src/threads.js?version=2020-12-16"></script>
+        <script src="src/objects.js?version=2020-12-16"></script>
         <script src="src/gui.js?version=2020-12-15"></script>
         <script src="src/paint.js?version=2020-05-17"></script>
         <script src="src/lists.js?version=2020-12-01"></script>
diff --git a/src/objects.js b/src/objects.js
index 92b3efd4..e9188079 100644
--- a/src/objects.js
+++ b/src/objects.js
@@ -84,7 +84,7 @@ BlockEditorMorph, BlockDialogMorph, PrototypeHatBlockMorph,  BooleanSlotMorph,
 localize, TableMorph, TableFrameMorph, normalizeCanvas, VectorPaintEditorMorph,
 AlignmentMorph, Process, WorldMap, copyCanvas, useBlurredShadows*/
 
-modules.objects = '2020-December-15';
+modules.objects = '2020-December-16';
 
 var SpriteMorph;
 var StageMorph;
@@ -928,6 +928,12 @@ SpriteMorph.prototype.initBlocks = function () {
             category: 'sensing',
             spec: 'frames'
         },
+        reportYieldCount: {
+            dev: true,
+            type: 'reporter',
+            category: 'sensing',
+            spec: 'yields'
+        },
         reportThreadCount: {
             dev: true,
             type: 'reporter',
@@ -2552,6 +2558,7 @@ SpriteMorph.prototype.blockTemplates = function (category) {
             blocks.push(block('reportThreadCount'));
             blocks.push(block('reportStackSize'));
             blocks.push(block('reportFrameCount'));
+            blocks.push(block('reportYieldCount'));
         }
 
 	/////////////////////////////////
@@ -8714,6 +8721,7 @@ StageMorph.prototype.blockTemplates = function (category) {
             blocks.push(block('reportThreadCount'));
             blocks.push(block('reportStackSize'));
             blocks.push(block('reportFrameCount'));
+            blocks.push(block('reportYieldCount'));
         }
 
     /////////////////////////////////
diff --git a/src/threads.js b/src/threads.js
index 7a425f8a..b85e5d40 100644
--- a/src/threads.js
+++ b/src/threads.js
@@ -61,7 +61,7 @@ StageMorph, SpriteMorph, StagePrompterMorph, Note, modules, isString, copy, Map,
 isNil, WatcherMorph, List, ListWatcherMorph, alert, console, TableMorph, BLACK,
 TableFrameMorph, ColorSlotMorph, isSnapObject, newCanvas, Symbol, SVG_Costume*/
 
-modules.threads = '2020-December-09';
+modules.threads = '2020-December-16';
 
 var ThreadManager;
 var Process;
@@ -584,6 +584,7 @@ function Process(topBlock, receiver, onComplete, yieldFirst) {
     this.isPaused = false;
     this.pauseOffset = null;
     this.frameCount = 0;
+    this.yieldCount = 0;
     this.exportResult = false;
     this.onComplete = onComplete || null;
     this.procedureCount = 0;
@@ -642,6 +643,7 @@ Process.prototype.runStep = function (deadline) {
         this.evaluateContext();
     }
 
+    this.yieldCount += 1;
     this.lastYield = Date.now();
     this.isFirstStep = false;
 
@@ -5925,6 +5927,10 @@ Process.prototype.reportFrameCount = function () {
     return this.frameCount;
 };
 
+Process.prototype.reportYieldCount = function () {
+    return this.yieldCount;
+};
+
 // Process single-stepping
 
 Process.prototype.flashContext = function () {