diff --git a/src/mdformat/_util.py b/src/mdformat/_util.py
index 24a3934..d95a2c0 100644
--- a/src/mdformat/_util.py
+++ b/src/mdformat/_util.py
@@ -66,9 +66,10 @@ def is_md_equal(
         html = mdit.render(text)
 
         # Remove codeblocks because code formatter plugins do arbitrary changes.
-        for codeclass in codeformatters:
+        if codeformatters:
+            langs_re = "|".join(re.escape(lang) for lang in codeformatters)
             html = re.sub(
-                f'<code class="language-{codeclass}">.*</code>',
+                rf'<code class="language-(?:{langs_re})">.*</code>',
                 "",
                 html,
                 flags=re.DOTALL,
diff --git a/tests/test_util.py b/tests/test_util.py
new file mode 100644
index 0000000..e3bc89f
--- /dev/null
+++ b/tests/test_util.py
@@ -0,0 +1,23 @@
+from mdformat._util import is_md_equal
+
+
+def test_is_md_equal():
+    md1 = """
+paragraph
+
+```js
+console.log()
+```
+
+paragr
+"""
+    md2 = """
+paragraph
+
+```js
+bonsole.l()g
+```
+
+paragr"""
+    assert not is_md_equal(md1, md2)
+    assert is_md_equal(md1, md2, codeformatters=("js", "go"))