diff --git a/src/blocks/scratch3_pen.js b/src/blocks/scratch3_pen.js
index 407215120..37609952f 100644
--- a/src/blocks/scratch3_pen.js
+++ b/src/blocks/scratch3_pen.js
@@ -7,6 +7,13 @@ const MathUtil = require('../util/math-util');
 const RenderedTarget = require('../sprites/rendered-target');
 const log = require('../util/log');
 
+/**
+ * Icon svg to be displayed at the left edge of each extension block, encoded as a data URI.
+ * @type {string}
+ */
+// eslint-disable-next-line max-len
+const iconURI = 'data:image/svg+xml;base64,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';
+
 /**
  * Enum for pen color parameters.
  * @readonly
@@ -235,6 +242,7 @@ class Scratch3PenBlocks {
         return {
             id: 'pen',
             name: 'Pen',
+            iconURI: iconURI,
             blocks: [
                 {
                     opcode: 'clear',
diff --git a/src/engine/runtime.js b/src/engine/runtime.js
index c86516bf7..56fceadfc 100644
--- a/src/engine/runtime.js
+++ b/src/engine/runtime.js
@@ -421,6 +421,7 @@ class Runtime extends EventEmitter {
         const categoryInfo = {
             id: extensionInfo.id,
             name: extensionInfo.name,
+            iconURI: extensionInfo.iconURI,
             color1: '#FF6680',
             color2: '#FF4D6A',
             color3: '#FF3355',
@@ -524,8 +525,21 @@ class Runtime extends EventEmitter {
         // but each `[ARG]` will need to be replaced with the number in this map instead of `args0.length`.
         const argsMap = {};
 
-        blockJSON.message0 = blockInfo.text.replace(/\[(.+?)]/g, (match, placeholder) => {
+        blockJSON.message0 = '';
 
+        // If an icon for the extension exists, prepend it to each block
+        if (categoryInfo.iconURI) {
+            blockJSON.message0 = '%1';
+            const iconJSON = {
+                type: 'field_image',
+                src: categoryInfo.iconURI,
+                width: 40,
+                height: 40
+            };
+            blockJSON.args0.push(iconJSON);
+        }
+
+        blockJSON.message0 += blockInfo.text.replace(/\[(.+?)]/g, (match, placeholder) => {
             // Sanitize the placeholder to ensure valid XML
             placeholder = placeholder.replace(/[<"&]/, '_');