diff --git a/application/src/Api/Adapter/SitePageAdapter.php b/application/src/Api/Adapter/SitePageAdapter.php
index 5a4fb6c83..dd1a042a1 100644
--- a/application/src/Api/Adapter/SitePageAdapter.php
+++ b/application/src/Api/Adapter/SitePageAdapter.php
@@ -228,8 +228,16 @@ private function hydrateBlocks(array $blockData, SitePage $page, ErrorStore $err
                 return;
             }
             if (!is_array($inputBlock['o:data'])) {
-                $errorStore->addError('o:block', 'Block data must not be a scalar value.'); // @translate
-                return;
+                // Attempt to convert the data to an array before returning with
+                // an error. This is needed in part so fallback blocks don't
+                // lose their data onced saved.
+                $blockData = json_decode($inputBlock['o:data'], true);
+                if (is_array($blockData)) {
+                    $inputBlock['o:data'] = $blockData;
+                } else {
+                    $errorStore->addError('o:block', 'Block data must not be a scalar value.'); // @translate
+                    return;
+                }
             }
 
             $block->setLayout($inputBlock['o:layout']);
diff --git a/application/src/Site/BlockLayout/Fallback.php b/application/src/Site/BlockLayout/Fallback.php
index 76d75feea..23b23021c 100644
--- a/application/src/Site/BlockLayout/Fallback.php
+++ b/application/src/Site/BlockLayout/Fallback.php
@@ -5,6 +5,7 @@
 use Omeka\Api\Representation\SitePageRepresentation;
 use Omeka\Api\Representation\SitePageBlockRepresentation;
 use Omeka\Stdlib\Message;
+use Laminas\Form\Element;
 use Laminas\View\Renderer\PhpRenderer;
 
 class Fallback extends AbstractBlockLayout
@@ -34,7 +35,10 @@ public function getLabel()
     public function form(PhpRenderer $view, SiteRepresentation $site,
         SitePageRepresentation $page = null, SitePageBlockRepresentation $block = null
     ) {
-        return $view->translate('This layout is invalid.');
+        // Preserve the original data.
+        $element = new Element\Hidden("o:block[__blockIndex__][o:data]");
+        $element->setValue(json_encode($block->data()));
+        return $view->translate('This layout is invalid.') . $view->formElement($element);
     }
 
     public function render(PhpRenderer $view, SitePageBlockRepresentation $block)