diff --git a/app/controllers/workspaces_controller.rb b/app/controllers/workspaces_controller.rb
index 4f25fe5..32ee33c 100644
--- a/app/controllers/workspaces_controller.rb
+++ b/app/controllers/workspaces_controller.rb
@@ -55,11 +55,25 @@ def update
     respond_to do |format|
       if @workspace.update(workspace_params)
         format.html { redirect_to @workspace, notice: update_notice }
-        format.json { render :show, status: :ok, location: @workspace }
-        format.js { render json: {}, status: :ok }
+        format.json do
+          # render :show, status: :ok, location: @workspace
+          # Handle an XHR request to save a workspace by returning the flash messages pre-rendered
+          flash.now[:notice] = update_notice
+          render json: { flash: render_to_string(partial: '/flash_messages', formats: [:html]), persistedState: @workspace.state }
+        end
+        format.js do
+          # Handle an XHR request to save a workspace by returning the flash messages pre-rendered
+          flash.now[:notice] = update_notice
+          render json: { flash: render_to_string(partial: '/flash_messages'), state: @workspace.state }
+        end
       else
         format.html { render :edit, status: :unprocessable_entity }
         format.json { render json: @workspace.errors, status: :unprocessable_entity }
+        format.js do
+          # Handle an XHR request to save a workspace by returning the flash messages pre-rendered
+          flash.now[:alert] = "Your workspace could not be saved: #{@workspace.errors}"
+          render partial: '/flash_messages'
+        end
       end
     end
   end
diff --git a/app/javascript/components/Viewer.js b/app/javascript/components/Viewer.js
index f85b6bd..58d4a0e 100644
--- a/app/javascript/components/Viewer.js
+++ b/app/javascript/components/Viewer.js
@@ -18,14 +18,15 @@ class Viewer extends React.Component {
   constructor() {
     super();
     this.state = {
-      currentState: {},
+      viewerState: {},
     };
   }
 
   /** */
   componentDidMount() {
     const {
-      annototEndpointUrl, config, enabledPlugins, state, updateStateSelector, projectResourcesUrl,
+      annototEndpointUrl, config, enabledPlugins, initialState,
+      viewerStateSelector, projectResourcesUrl,
     } = this.props;
 
     delete config.export;
@@ -48,11 +49,11 @@ class Viewer extends React.Component {
       ],
     );
 
-    if (state) {
+    if (initialState) {
       instance.store.dispatch(
         importMiradorState(
           {
-            ...state,
+            ...initialState,
             config: instance.store.getState().config,
           },
         ),
@@ -60,14 +61,14 @@ class Viewer extends React.Component {
     }
 
     if (projectResourcesUrl) instance.store.dispatch(addResource(projectResourcesUrl));
-    if (updateStateSelector) {
+    if (viewerStateSelector) {
       instance.store.subscribe(() => {
-        const currentState = instance.store.getState();
-        const exportableState = getExportableState(currentState);
-        this.setState({ currentState: exportableState });
-        const inputElement = document.querySelector(updateStateSelector);
+        const viewerState = instance.store.getState();
+        const exportableState = getExportableState(viewerState);
+        this.setState({ viewerState: exportableState });
+        const inputElement = document.querySelector(viewerStateSelector);
         const __mise_cache__ = { // eslint-disable-line camelcase
-          manifests: mapValues(currentState.manifests, m => this.getManifestCache(currentState, m)),
+          manifests: mapValues(viewerState.manifests, m => this.getManifestCache(viewerState, m)),
         };
         if (inputElement) {
           inputElement.value = JSON.stringify(
@@ -112,22 +113,30 @@ class Viewer extends React.Component {
   }
 
   checkUnsavedChanges = (event) => {
-    const { currentState } = this.state;
-    const { state: initialState, saveInProgressSelector } = this.props;
-    // Skip checking for unsaved changes because a save is in progress
-    if (document.querySelector(saveInProgressSelector).value === 'true') return true;
+    const { viewerState } = this.state;
+    const { persistedStateSelector } = this.props;
+    // Get current persisted value of DOM element instead of using what is
+    // stuffed in props since the former may have been updated by a
+    // user-initiated save operation
+    const persistedState = document.querySelector(persistedStateSelector).value;
 
-    const expectedDiffPaths = ['__mise_cache__', 'config.annotation', 'config.export', 'workspace.id'];
     // Diff the two Mirador states
-    const difference = diff(initialState, currentState);
+    const difference = diff(persistedState, viewerState);
     // Remove known false positives from diff object
-    const filtered = omit(difference, expectedDiffPaths);
-    // Remove empty top-level objects created by prior call to omit
+    const filtered = omit(difference, ['__mise_cache__', 'config.annotation', 'config.export', 'workspace.id']);
+    // Remove empty top-level objects created by removing false positives
     const changes = omitBy(filtered, isEmpty);
+
     if (!isEmpty(changes)) {
+      console.dir(changes);
       event.preventDefault();
       event.returnValue = 'If you navigate away from the workspace now, changes you have made will be lost. Are you sure you want to navigate away?'; // eslint-disable-line no-param-reassign
       return event.returnValue;
+    } else {
+      console.log('client state:');
+      console.dir(viewerState);
+      console.log('server state:');
+      console.dir(persistedState);
     }
     return true;
   }
@@ -143,20 +152,20 @@ Viewer.propTypes = {
   annototEndpointUrl: PropTypes.string,
   config: PropTypes.object, // eslint-disable-line react/forbid-prop-types
   enabledPlugins: PropTypes.array, // eslint-disable-line react/forbid-prop-types
+  initialState: PropTypes.object, // eslint-disable-line react/forbid-prop-types
+  persistedStateSelector: PropTypes.string,
   projectResourcesUrl: PropTypes.string,
-  saveInProgressSelector: PropTypes.string,
-  state: PropTypes.object, // eslint-disable-line react/forbid-prop-types
-  updateStateSelector: PropTypes.string,
+  viewerStateSelector: PropTypes.string,
 };
 
 Viewer.defaultProps = {
   annototEndpointUrl: null,
   config: {},
   enabledPlugins: [],
+  initialState: null,
+  persistedStateSelector: null,
   projectResourcesUrl: null,
-  saveInProgressSelector: null,
-  state: null,
-  updateStateSelector: null,
+  viewerStateSelector: null,
 };
 
 export default Viewer;
diff --git a/app/javascript/controllers/save_workspace_controller.js b/app/javascript/controllers/save_workspace_controller.js
deleted file mode 100644
index b218861..0000000
--- a/app/javascript/controllers/save_workspace_controller.js
+++ /dev/null
@@ -1,9 +0,0 @@
-import { Controller } from 'stimulus';
-
-export default class extends Controller {
-  static targets = ['field'];
-
-  markSaveInProgress() {
-    this.fieldTarget.value = true;
-  }
-}
diff --git a/app/javascript/controllers/workspace_controller.js b/app/javascript/controllers/workspace_controller.js
new file mode 100644
index 0000000..1fe9de0
--- /dev/null
+++ b/app/javascript/controllers/workspace_controller.js
@@ -0,0 +1,11 @@
+import { Controller } from 'stimulus';
+
+export default class extends Controller {
+  static targets = ['flash', 'persistedState'];
+
+  updateForm(event) {
+    const { flash, persistedState } = event.detail[0];
+    this.persistedStateTarget.value = JSON.stringify(persistedState);
+    this.flashTarget.innerHTML = flash;
+  }
+}
diff --git a/app/views/layouts/_flash_messages.html.erb b/app/views/_flash_messages.html.erb
similarity index 100%
rename from app/views/layouts/_flash_messages.html.erb
rename to app/views/_flash_messages.html.erb
diff --git a/app/views/layouts/application.html.erb b/app/views/layouts/application.html.erb
index 214dca9..3aa14f4 100644
--- a/app/views/layouts/application.html.erb
+++ b/app/views/layouts/application.html.erb
@@ -10,7 +10,7 @@
     <%= javascript_pack_tag 'application', 'data-turbolinks-track': 'reload' %>
   </head>
 
-  <body data-controller='show-modal'>
+  <body data-controller='show-modal workspace'>
     <%= render 'layouts/navbar' %>
     <div class="main-content <%= 'with-sidebar' if content_for?(:sidebar) %>">
       <% if content_for?(:sidebar) %>
@@ -20,7 +20,9 @@
       <% end %>
 
       <main class='col py-4 pe-4'>
-        <%= render 'layouts/flash_messages' %>
+        <div class="flash_container" data-workspace-target="flash">
+          <%= render '/flash_messages' %>
+        </div>
 
         <%= content_for(:top_level_nav) if content_for?(:top_level_nav) %>
 
diff --git a/app/views/workspaces/viewer.html.erb b/app/views/workspaces/viewer.html.erb
index 0f574f1..cf1cb54 100644
--- a/app/views/workspaces/viewer.html.erb
+++ b/app/views/workspaces/viewer.html.erb
@@ -6,10 +6,15 @@
     <% if can? :update, @workspace %>
       <%= react_component("EditInPlace", { field: 'title', value: @workspace.title, csrfToken: form_authenticity_token, url: url_for(@workspace) }, tag: 'h1') %>
 
-      <%= form_with(model: @workspace, class: 'me-2', data: { controller: 'save-workspace' }) do |form| %>
-        <%= form.hidden_field :state %>
-        <%= form.hidden_field :save_in_progress, value: false, data: { save_workspace_target: 'field' } %>
-        <%= form.submit 'Save workspace', class: 'btn btn-primary', data: { action: 'save-workspace#markSaveInProgress' } %>
+      <%=
+        form_with(model: @workspace, class: 'me-2', local: false, data: {
+          action: 'ajax:success->workspace#updateForm ajax:error->workspace#updateForm',
+          type: :json
+        }) do |form|
+      %>
+        <%= form.hidden_field :viewer_state, data: { workspace_target: 'viewerState' } %>
+        <%= form.hidden_field :persisted_state, data: { workspace_target: 'persistedState' } %>
+        <%= form.submit 'Save workspace', class: 'btn btn-primary' %>
       <% end %>
     <% else %>
       <h1><%= @workspace.title %></h1>
@@ -21,20 +26,20 @@
 <div class="<%= @embed ? 'embedded-mirador-container' : 'mirador-container mx-2' %>">
   <% viewer_props = if can?(:update, @workspace) && !@embed
         {
+          annototEndpointUrl: project_annotations_url(@workspace.project),
           config: { id: "m-#{SecureRandom.hex}" }.deep_merge(@workspace.state&.dig('config') || {}),
           enabledPlugins: ['annotations'],
-          state: @workspace.state,
-          updateStateSelector: '#workspace_state',
-          saveInProgressSelector: '#workspace_save_in_progress',
+          initialState: @workspace.state,
+          persistedStateSelector: '#workspace_persisted_state',
           projectResourcesUrl: iiif_project_resources_url(@workspace.project),
-          annototEndpointUrl: project_annotations_url(@workspace.project),
+          viewerStateSelector: '#workspace_viewer_state',
         }
       else
         {
+          annototEndpointUrl: project_annotations_url(@workspace.project),
           config: { id: "m-#{SecureRandom.hex}" }.deep_merge(@workspace.embedded_workspace_config || {}),
           enabledPlugins: ['annotations'],
-          state: @workspace.state,
-          annototEndpointUrl: project_annotations_url(@workspace.project),
+          initialState: @workspace.state,
         }
       end
   %>