diff --git a/.github/workflows/python-package.yml b/.github/workflows/python-package.yml
index 44932a3..bef59ed 100644
--- a/.github/workflows/python-package.yml
+++ b/.github/workflows/python-package.yml
@@ -69,7 +69,7 @@ jobs:
 
       - run: |
           mk python-release owner=vkottler \
-                            repo=svgen version=0.6.3
+                            repo=svgen version=0.6.4
         if: |
           matrix.python-version == '3.11'
           && matrix.system == 'ubuntu-latest'
diff --git a/README.md b/README.md
index f67b997..826510b 100644
--- a/README.md
+++ b/README.md
@@ -2,11 +2,11 @@
     =====================================
     generator=datazen
     version=3.1.4
-    hash=9032a8122f42767cd7546b44a632c4c3
+    hash=e21b336d2e615b1fdad0bb7a28fc9fb8
     =====================================
 -->
 
-# svgen ([0.6.3](https://pypi.org/project/svgen/))
+# svgen ([0.6.4](https://pypi.org/project/svgen/))
 
 [![python](https://img.shields.io/pypi/pyversions/svgen.svg)](https://pypi.org/project/svgen/)
 ![Build Status](https://github.com/vkottler/svgen/workflows/Python%20Package/badge.svg)
diff --git a/local/variables/package.yaml b/local/variables/package.yaml
index edd7d3f..8b03069 100644
--- a/local/variables/package.yaml
+++ b/local/variables/package.yaml
@@ -1,5 +1,5 @@
 ---
 major: 0
 minor: 6
-patch: 3
+patch: 4
 entry: svgen
diff --git a/pyproject.toml b/pyproject.toml
index 8a3cb84..b93b407 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta:__legacy__"
 
 [project]
 name = "svgen"
-version = "0.6.3"
+version = "0.6.4"
 description = "A tool for working with scalable vector graphics."
 readme = "README.md"
 requires-python = ">=3.10"
diff --git a/svgen/__init__.py b/svgen/__init__.py
index c83f5ad..23561fe 100644
--- a/svgen/__init__.py
+++ b/svgen/__init__.py
@@ -1,7 +1,7 @@
 # =====================================
 # generator=datazen
 # version=3.1.4
-# hash=2bfa379dd491847550ef6405489ea06b
+# hash=4e1af49f6773895ec34a2d5ceb111420
 # =====================================
 
 """
@@ -10,4 +10,4 @@
 
 DESCRIPTION = "A tool for working with scalable vector graphics."
 PKG_NAME = "svgen"
-VERSION = "0.6.3"
+VERSION = "0.6.4"
diff --git a/svgen/element/__init__.py b/svgen/element/__init__.py
index 09acc07..13069d2 100644
--- a/svgen/element/__init__.py
+++ b/svgen/element/__init__.py
@@ -60,12 +60,13 @@ def __init__(
 
         self.children: List[Element] = children
 
-    def add_class(self, data: str) -> None:
+    def add_class(self, *data: str) -> None:
         """Add a class string."""
 
         raw = self["class"]
         classes = set(raw.split())
-        classes.add(data)
+        for item in data:
+            classes.add(item)
         self["class"] = " ".join(classes)
 
     def __setitem__(self, tag: str, value: AttributeValue) -> None:
diff --git a/tests/element/test_element.py b/tests/element/test_element.py
index 97fc217..bf7fdcd 100644
--- a/tests/element/test_element.py
+++ b/tests/element/test_element.py
@@ -25,6 +25,10 @@ def test_element_class():
     elem = Element(tag="div")
     assert elem["class"] == ""
 
+    elem.add_class("a", "b")
+    val = elem["class"]
+    assert val in {"a b", "b a"}
+
 
 def test_element_basic():
     """Test the element interface."""