diff --git a/src/engine/runtime.js b/src/engine/runtime.js
index 1393ee26913..adfffa78cf4 100644
--- a/src/engine/runtime.js
+++ b/src/engine/runtime.js
@@ -1408,13 +1408,13 @@ class Runtime extends EventEmitter {
             if (!blockInfo.disableMonitor && context.inputList.length === 0) {
                 blockJSON.checkboxInFlyout = true;
             }
-        } else if (blockInfo.blockType === BlockType.LOOP) {
+        } else if (blockInfo.blockType === BlockType.LOOP || blockInfo.branchIconURI) {
             // Add icon to the bottom right of a loop block
             blockJSON[`lastDummyAlign${outLineNum}`] = 'RIGHT';
             blockJSON[`message${outLineNum}`] = '%1';
             blockJSON[`args${outLineNum}`] = [{
                 type: 'field_image',
-                src: './static/blocks-media/repeat.svg', // TODO: use a constant or make this configurable?
+                src: blockInfo.branchIconURI || './static/blocks-media/repeat.svg',
                 width: 24,
                 height: 24,
                 alt: '*', // TODO remove this since we don't use collapsed blocks in scratch
diff --git a/test/unit/tw_branch_icon_uri.js b/test/unit/tw_branch_icon_uri.js
new file mode 100644
index 00000000000..2de54dab606
--- /dev/null
+++ b/test/unit/tw_branch_icon_uri.js
@@ -0,0 +1,39 @@
+const {test} = require('tap');
+const VirtualMachine = require('../../src/virtual-machine');
+const BlockType = require('../../src/extension-support/block-type');
+
+test('branchIconURI', t => {
+    const vm = new VirtualMachine();
+    vm.extensionManager._registerInternalExtension({
+        getInfo: () => ({
+            id: 'testextension',
+            name: 'test',
+            blocks: [
+                {
+                    blockType: BlockType.LOOP,
+                    opcode: 'block1',
+                    text: 'no custom icon'
+                },
+                {
+                    blockType: BlockType.LOOP,
+                    opcode: 'block2',
+                    text: 'LOOP with custom icon',
+                    branchIconURI: 'data:whatever1'
+                },
+                {
+                    blockType: BlockType.CONDITIONAL,
+                    opcode: 'block2',
+                    text: 'CONDITIONAL with custom icon',
+                    branchIconURI: 'data:whatever2'
+                }
+            ]
+        })
+    });
+
+    const blocks = vm.runtime.getBlocksJSON();
+    t.equal(blocks[0].args2[0].src, './static/blocks-media/repeat.svg', 'default custom icon');
+    t.equal(blocks[1].args2[0].src, 'data:whatever1', 'LOOP with custom icon');
+    t.equal(blocks[2].args2[0].src, 'data:whatever2', 'CONDITIONAL with custom icon');
+
+    t.end();
+});