diff --git a/mdit_py_plugins/amsmath/__init__.py b/mdit_py_plugins/amsmath/__init__.py
index 197f1cc..5aa82bb 100644
--- a/mdit_py_plugins/amsmath/__init__.py
+++ b/mdit_py_plugins/amsmath/__init__.py
@@ -68,7 +68,7 @@ def amsmath_plugin(md: MarkdownIt, *, renderer: Optional[Callable[[str], str]] =
         {"alt": ["paragraph", "reference", "blockquote", "list", "footnote_def"]},
     )
 
-    _renderer = lambda content: escapeHtml(content) if renderer is None else renderer
+    _renderer = (lambda content: escapeHtml(content)) if renderer is None else renderer
 
     def render_amsmath_block(self, tokens, idx, options, env):
         content = _renderer(str(tokens[idx].content))
diff --git a/tests/test_amsmath.py b/tests/test_amsmath.py
index 55b4987..fe48cf1 100644
--- a/tests/test_amsmath.py
+++ b/tests/test_amsmath.py
@@ -27,6 +27,23 @@ def test_plugin_parse(data_regression):
     data_regression.check([t.as_dict() for t in tokens])
 
 
+def test_custom_renderer(data_regression):
+    md = MarkdownIt().use(amsmath_plugin, renderer=lambda x: x + "!")
+    output = md.render("\\begin{equation}\na\n\\end{equation}")
+    assert (
+        output.strip()
+        == dedent(
+            """\
+        <div class="math amsmath">
+        \\begin{equation}
+        a
+        \\end{equation}!
+        </div>
+        """
+        ).strip()
+    )
+
+
 @pytest.mark.parametrize(
     "line,title,input,expected",
     read_fixture_file(FIXTURE_PATH.joinpath("fixtures", "amsmath.md")),