diff --git a/pytools/graph.py b/pytools/graph.py
index 359e8060e3b0e594b82e5886102ede126d01573e..a091d95d38b01d0f14fe0c4324b5fa72917e66d8 100644
--- a/pytools/graph.py
+++ b/pytools/graph.py
@@ -28,7 +28,6 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 """
 
-
 __doc__ = """
 Graph Algorithms
 ================
@@ -54,6 +53,10 @@ Graph Algorithms
 Type Variables Used
 -------------------
 
+.. class:: _SupportsLT
+
+    A :class:`~typing.Protocol` for `__lt__` support.
+
 .. class:: NodeT
 
     Type of a graph node, can be any hashable type.