diff --git a/sumpy/expansion/__init__.py b/sumpy/expansion/__init__.py
index df39c7661f8b382f328e429ee0c84f9c94f6b759..b82be282948613f0e5f94a26a7ad8c201d4e45f5 100644
--- a/sumpy/expansion/__init__.py
+++ b/sumpy/expansion/__init__.py
@@ -407,7 +407,7 @@ class LinearPDEBasedExpansionTermsWrangler(ExpansionTermsWrangler):
     .. automethod:: __init__
     """
 
-    init_arg_names = ("order", "dim", "max_mi")
+    init_arg_names = ("order", "dim", "knl", "max_mi")
 
     def __init__(self, order, dim, knl, max_mi=None):
         r"""