diff --git a/rich/markdown.py b/rich/markdown.py
index 3ab4af0e..704da301 100644
--- a/rich/markdown.py
+++ b/rich/markdown.py
@@ -254,10 +254,9 @@ class TableElement(MarkdownElement):
     ) -> RenderResult:
         table = Table(box=box.SIMPLE_HEAVY)
 
-        assert self.header is not None
-        assert self.header.row is not None
-        for column in self.header.row.cells:
-            table.add_column(column.content)
+        if self.header is not None and self.header.row is not None:
+            for column in self.header.row.cells:
+                table.add_column(column.content)
 
         if self.body is not None:
             for row in self.body.rows: