diff --git a/markdownify/__init__.py b/markdownify/__init__.py
index cc3d153..c34e57e 100644
--- a/markdownify/__init__.py
+++ b/markdownify/__init__.py
@@ -315,6 +315,9 @@ def convert_hn(self, n, el, text, convert_as_inline):
         if convert_as_inline:
             return text
 
+        # prevent MemoryErrors in case of very large n
+        n = max(1, min(6, n))
+
         style = self.options['heading_style'].lower()
         text = text.strip()
         if style == UNDERLINED and n <= 2:
diff --git a/tests/test_conversions.py b/tests/test_conversions.py
index 0be1d0c..1c5f9c2 100644
--- a/tests/test_conversions.py
+++ b/tests/test_conversions.py
@@ -133,6 +133,7 @@ def test_hn():
     assert md('<h4>Hello</h4>') == '\n#### Hello\n\n'
     assert md('<h5>Hello</h5>') == '\n##### Hello\n\n'
     assert md('<h6>Hello</h6>') == '\n###### Hello\n\n'
+    assert md('<h10>Hello</h10>') == md('<h6>Hello</h6>')
 
 
 def test_hn_chained():