diff --git a/application/src/Site/BlockLayout/TableOfContents.php b/application/src/Site/BlockLayout/TableOfContents.php
index 5d80c44ce..dd1d01d11 100644
--- a/application/src/Site/BlockLayout/TableOfContents.php
+++ b/application/src/Site/BlockLayout/TableOfContents.php
@@ -20,7 +20,14 @@ public function form(PhpRenderer $view, SiteRepresentation $site,
     ) {
         $depth = new Number("o:block[__blockIndex__][o:data][depth]");
 
-        $depth->setValue($block ? $block->dataValue('depth', 1) : 1);
+        $depthValue = 1;
+        if ($block) {
+            $blockDepth = (int) $block->dataValue('depth');
+            if ($blockDepth > 1) {
+                $depthValue = $blockDepth;
+            }
+        }
+        $depth->setValue($depthValue);
         $depth->setAttribute('min', 1);
 
         $html = '';
@@ -53,7 +60,11 @@ public function render(PhpRenderer $view, SitePageBlockRepresentation $block, $t
         }
         $subNav = new Navigation($newPages);
 
-        $depth = $block->dataValue('depth', 1);
+        // Don't use dataValue's default here; we need to handle empty/non-numerics anyway
+        $depth = (int) $block->dataValue('depth');
+        if ($depth < 1) {
+            $depth = 1;
+        }
 
         return $view->partial($templateViewScript, [
             'block' => $block,