diff --git a/packages/scratch-gui/src/containers/blocks.jsx b/packages/scratch-gui/src/containers/blocks.jsx
index f5ea9d561b..6a8efb9730 100644
--- a/packages/scratch-gui/src/containers/blocks.jsx
+++ b/packages/scratch-gui/src/containers/blocks.jsx
@@ -165,6 +165,10 @@ class Blocks extends React.Component {
         );
     }
     componentDidUpdate (prevProps) {
+        if (this.props.useCatBlocks !== prevProps.useCatBlocks) {
+            this.ScratchBlocks = VMScratchBlocks(this.props.vm, this.props.useCatBlocks);
+        }
+
         // If any modals are open, call hideChaff to close z-indexed field editors
         if (this.props.anyModalVisible && !prevProps.anyModalVisible) {
             this.ScratchBlocks.hideChaff();
@@ -699,7 +703,7 @@ const mapStateToProps = state => ({
     toolboxXML: state.scratchGui.toolbox.toolboxXML,
     customProceduresVisible: state.scratchGui.customProcedures.active,
     workspaceMetrics: state.scratchGui.workspaceMetrics,
-    useCatBlocks: isTimeTravel2020(state)
+    useCatBlocks: isTimeTravel2020(state) || state.scratchGui.theme.theme === 'high-contrast'
 });
 
 const mapDispatchToProps = dispatch => ({
diff --git a/packages/scratch-gui/src/lib/blocks.js b/packages/scratch-gui/src/lib/blocks.js
index 14fafc92c9..4468b85d36 100644
--- a/packages/scratch-gui/src/lib/blocks.js
+++ b/packages/scratch-gui/src/lib/blocks.js
@@ -5,7 +5,10 @@
  * @returns {ScratchBlocks} ScratchBlocks connected with the vm
  */
 export default function (vm, useCatBlocks) {
-    const ScratchBlocks = useCatBlocks ? require('cat-blocks') : require('scratch-blocks');
+    const ScratchBlocks = require('scratch-blocks');
+
+    ScratchBlocks.useCatBlocks = useCatBlocks;
+    
     const jsonForMenuBlock = function (name, menuOptionsFn, colors, start) {
         return {
             message0: '%1',