diff --git a/HISTORY.md b/HISTORY.md
index 4bd3a571..73d4e2a6 100755
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -16,7 +16,7 @@
     * new MOUSE POSITION primitive reporter in the SENSING category
     * new "position" choice in OF reporter's attribute dropdown, reports a list of XY coordinates
     * new "categories" choice in MY reporter's dropdown, reports an ordered list of all category names whose indices match the "category" reported elsewhere
-    * new "label", "type", "scope", "slots", "menus" and "editables" choices in the OF BLOCK block-attribute reporter's dropdown
+    * new "label", "type", "scope", "slots", "defaults", "menus" and "editables" choices in the OF BLOCK block-attribute reporter's dropdown
     * new "set attribute of block" primitive, experimental
     * new "define block" primitive, experimental
     * new "this script" primitive, experimental
@@ -58,6 +58,7 @@
 * German translation update for "menus"
 * blocks, threads: new "editables" selector for block attributes (indicates read-only input slots)
 * German translation update for "editables"
+* blocks, threads: new "defaults" selector for block attributes
 
 ### 2022-06-27
 * threads: trim block label before identifying existing definition in DEFINE
diff --git a/src/blocks.js b/src/blocks.js
index cdaaa3af..5d033af2 100644
--- a/src/blocks.js
+++ b/src/blocks.js
@@ -809,6 +809,7 @@ SyntaxElementMorph.prototype.labelParts = {
             'type': ['type'],
             'scope': ['scope'],
             'slots': ['slots'],
+            'defaults': ['defaults'],
             'menus' : ['menus'],
             'editables' : ['editables']
         }
@@ -823,6 +824,7 @@ SyntaxElementMorph.prototype.labelParts = {
             'type': ['type'],
             'scope': ['scope'],
             'slots': ['slots'],
+            'defaults': ['defaults'],
             'menus' : ['menus'],
             'editables' : ['editables']
         }
diff --git a/src/threads.js b/src/threads.js
index fc2740b5..04f30397 100644
--- a/src/threads.js
+++ b/src/threads.js
@@ -5663,6 +5663,15 @@ Process.prototype.reportBasicBlockAttribute = function (attribute, block) {
                     each.getSlotSpec() : each.getSpec()
             )
         ).map(spec => this.slotType(spec));
+    case 'defaults':
+        slots = new List();
+        if (expr.isCustomBlock) {
+            def = (expr.isGlobal ?
+                expr.definition
+                : this.blockReceiver().getMethod(expr.semanticSpec));
+            def.declarations.forEach(value => slots.add(value[1]));
+        }
+        return slots;
     case 'menus':
         slots = new List();
         if (expr.isCustomBlock) {
@@ -5964,6 +5973,19 @@ Process.prototype.doSetBlockAttribute = function (attribute, block, val) {
             }
         });
         break;
+    case 'defaults':
+        this.assertType(val, ['list', 'Boolean', 'number', 'text']);
+        if (!(val instanceof List)) {
+            val = new List([val]);
+        }
+        def.inputNames().forEach((name, idx) => {
+            var info = def.declarations.get(name),
+                options = val.at(idx + 1);
+            this.assertType(options, ['Boolean', 'number', 'text']);
+            info[1] = options;
+            def.declarations.set(name, info);
+        });
+        break;
     case 'menus':
         this.assertType(val, ['list', 'text', 'number']);
         if (!(val instanceof List)) {