diff --git a/app/index.html b/app/index.html
index c813133..656fe37 100644
--- a/app/index.html
+++ b/app/index.html
@@ -1200,6 +1200,7 @@ body {
     //   - Otherwise: hide
     if (!categoriesUse) return true;
     if (page.file === defaultPage()) return true;
+    if (page.uncategorized) return true;
     const variants = page.variants || [];
     if (variants.includes(activeCategory)) return true;
     const cat = categoriesByCode[activeCategory];
@@ -1602,7 +1603,7 @@ function fmtDatetime(dtStr) {
 
     // Category filter
     if (categoriesUse && activeCategory) {
-      posts = posts.filter(function(e) { return e.category === activeCategory; });
+      posts = posts.filter(function(e) { return !e.category || e.category === activeCategory; });
     }
 
     // Field filter
@@ -2245,7 +2246,7 @@ function fmtDatetime(dtStr) {
       ? navData.find(p => p.file === currentPage)
       : null;
     categoriesList.forEach(cat => {
-      const hasVariant = !page || !page.variants || page.variants.includes(cat.code);
+      const hasVariant = !page || page.uncategorized || !(page.variants && page.variants.length) || page.variants.includes(cat.code);
       const hasMsg = !!cat.notfoundmessage;
       if (hasVariant || hasMsg || cat.code === activeCategory) out.add(cat.code);
     });
@@ -2272,7 +2273,7 @@ function fmtDatetime(dtStr) {
         'data-code': cat.code
       });
       option.appendChild(document.createTextNode(primary));
-      const hasVariant = !page || !page.variants || page.variants.includes(cat.code);
+      const hasVariant = !page || page.uncategorized || !(page.variants && page.variants.length) || page.variants.includes(cat.code);
       if (!hasVariant && cat.notfoundmessage) {
         option.appendChild(el('span', { className: 'secondary', textContent: cat.notfoundmessage }));
       } else if (secondary) {
diff --git a/mdcms.py b/mdcms.py
index 7050c9e..b50ebb5 100644
--- a/mdcms.py
+++ b/mdcms.py
@@ -266,10 +266,14 @@ def build_page_nav(
         }
         if categories_use:
             covered = {}
+            has_uncategorized = False
             for code, record in variants.items():
-                key = code if code is not None else default_code
-                if key:
-                    covered[key] = record.get("title", "")
+                if code is None:
+                    has_uncategorized = True
+                else:
+                    covered[code] = record.get("title", "")
+            if has_uncategorized:
+                entry["uncategorized"] = True
             entry["variants"] = sorted(covered.keys())
             entry["titles"] = covered
         out.append(entry)
@@ -313,6 +317,8 @@ def generate_nav_yml(sections: list, pages: list, categories_use: bool = False)
             if p.get("section-id"):
                 lines.append(f"    section-id: {p['section-id']}")
             lines.append(f"    sort: {p.get('sort', 100)}")
+            if categories_use and p.get("uncategorized"):
+                lines.append("    uncategorized: true")
             if categories_use and p.get("variants"):
                 lines.append(f"    variants: [{', '.join(p['variants'])}]")
             if categories_use and p.get("titles"):
@@ -344,8 +350,7 @@ def generate_search_json(
             "body": r.get("body", ""),
         }
         if categories_use:
-            code = r.get("code")
-            entry["category"] = code if code is not None else default_code
+            entry["category"] = r.get("code")  # None → null = show in all categories
         out.append(entry)
     return json.dumps(out, indent=2, ensure_ascii=False)