diff --git a/js/common/model/CompareBlockSetModel.ts b/js/common/model/CompareBlockSetModel.ts
index 7b8c7456..119d6d4d 100644
--- a/js/common/model/CompareBlockSetModel.ts
+++ b/js/common/model/CompareBlockSetModel.ts
@@ -151,7 +151,7 @@ export default class CompareBlockSetModel extends BlockSetModel<BlockSet> {
 
                // We must undefer the Cube's materialProperty first, in order for the DynamicProperty in DensityAccordionBox to be correctly unregistered
                // We do not know why scheduling a NOTIFY order dependency was not sufficient
-               // TODO: We may not need these anymore, https://github.com/phetsims/density-buoyancy-common/issues/273
+               // TODO: We may not need these anymore, https://github.com/phetsims/density-buoyancy-common/issues/280
                propertyStateHandlerSingleton.registerPhetioOrderDependency( cube.materialProperty, PropertyStatePhase.UNDEFER, model.blockSetProperty, PropertyStatePhase.UNDEFER );
                return cube;
              } ) :
@@ -260,10 +260,13 @@ export default class CompareBlockSetModel extends BlockSetModel<BlockSet> {
     const options = combineOptions<StrictCubeOptions>( {
       customMaterialOptions: {
         density: initialDensity,
+        densityPropertyOptions: {
+          phetioReadOnly: true
+        },
         colorProperty: densityAdjustedColorProperty
       },
       materialPropertyOptions: {
-        phetioReadOnly: true // TODO: And readonly density!!! https://github.com/phetsims/density-buoyancy-common/issues/273
+        phetioReadOnly: true
       },
       availableMassMaterials: [
         ...initialMaterials,