Fix grouping: this is how I intended it, misguided as I was in boolean
operator associativity.
diff --git a/Objects/abstract.c b/Objects/abstract.c
index e3492ec..fcd86ca 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -813,8 +813,8 @@
 					PyNumber_Add, 0) <= 0)
 			return x;
 	}
-	else if ((HASINPLACE(v)
-		  && (v->ob_type->tp_as_sequence != NULL &&
+	else if (HASINPLACE(v)
+		  && ((v->ob_type->tp_as_sequence != NULL &&
 		      (f = v->ob_type->tp_as_sequence->sq_inplace_concat) != NULL))
 		 || (v->ob_type->tp_as_number != NULL &&
 		     (f = v->ob_type->tp_as_number->nb_inplace_add) != NULL))