diff --git a/_msprimemodule.c b/_msprimemodule.c
index 8eb2e59bb..521d7586a 100644
--- a/_msprimemodule.c
+++ b/_msprimemodule.c
@@ -2463,8 +2463,9 @@ static PyMethodDef TreeSequence_methods[] = {
         "Returns the sample size" },
     {"get_population", (PyCFunction) TreeSequence_get_population, METH_VARARGS,
         "Returns the population associated with the specified node." },
-    {"get_pairwise_diversity", (PyCFunction) TreeSequence_get_pairwise_diversity,
-        METH_VARARGS, "Returns the average pairwise diversity." },
+    {"get_pairwise_diversity",
+        (PyCFunction) TreeSequence_get_pairwise_diversity,
+        METH_VARARGS|METH_KEYWORDS, "Returns the average pairwise diversity." },
     {"get_simulation_parameters",
         (PyCFunction) TreeSequence_get_simulation_parameters, METH_NOARGS,
         "Returns the simulation parameters encoded as JSON." },