diff --git a/dirty_equals/_base.py b/dirty_equals/_base.py
index 9481a8f..e447619 100644
--- a/dirty_equals/_base.py
+++ b/dirty_equals/_base.py
@@ -277,8 +277,10 @@ def __init__(self, expected_value: Any, *more_expected_values: Any):
 
         assert 1 == IsOneOf(1, 2, 3)
         assert 4 != IsOneOf(1, 2, 3)
+        # check that a list either contain 1 or is empty
         assert [1, 2, 3] == Contains(1) | IsOneOf([])
         assert [] == Contains(1) | IsOneOf([])
+        ```
         """
         self.expected_values: Tuple[Any, ...] = (expected_value,) + more_expected_values
         super().__init__(*self.expected_values)
diff --git a/tests/test_docs.py b/tests/test_docs.py
index eeb9a26..cb325b4 100644
--- a/tests/test_docs.py
+++ b/tests/test_docs.py
@@ -29,6 +29,12 @@ def _import_execute(module_name: str, source: str, rewrite_assertions: bool = Fa
 
 def extract_code_chunks(path: Path, text: str, offset: int):
     rel_path = path.relative_to(ROOT_DIR)
+    fences = len(re.findall(r'^```', text, flags=re.M))
+    if fences % 2 != 0:
+        raise ValueError(
+            f'{rel_path}:{offset} has an odd number of code fences (```), might be missing a closing fence'
+        )
+
     for m_code in re.finditer(r'^```(.*?)$\n(.*?)^```', text, flags=re.M | re.S):
         prefix = m_code.group(1).lower()
         if not prefix.startswith(('py', '{.py')) or 'test="false"' in prefix: