diff --git a/rhodecode/lib/markup_renderer.py b/rhodecode/lib/markup_renderer.py
--- a/rhodecode/lib/markup_renderer.py
+++ b/rhodecode/lib/markup_renderer.py
@@ -539,18 +539,27 @@ class MarkupRenderer(object):
             return body, resources
 
         captured_errors = {}
+        error_body = """
+                        <div style="text-align: center;">
+                            <h3>Invalid Notebook!</h3>
+                            <p>{}</p>
+                        </div>
+                    """
         # TODO: In the event of a newer jupyter notebook version, consider increasing the as_version parameter
         notebook = nbformat.reads(source, as_version=4, capture_validation_error=captured_errors)
         if captured_errors:
             error_messages = '<br>'.join(str(error) for error in captured_errors.values())
-            body = f"""
-                    <div style="text-align: center;">
-                        <h3>Invalid Notebook!</h3>
-                        <p>{error_messages}</p>
-                    </div>
-                """
+            body = error_body.format(error_messages)
         else:
-            body, _ = as_html(notebook)
+            try:
+                body, _ = as_html(notebook)
+            except AttributeError:
+                try:
+                    nbformat.validate(nbformat.reader.reads(source))
+                except nbformat.ValidationError as exc:
+                    body = error_body.format(str(exc))
+                else:
+                    raise
         return body