diff --git a/sumpy/expansion/__init__.py b/sumpy/expansion/__init__.py
index 673b595b973a2a16e244140a6ffe4ac096e61b07..1010483f153b96c3b1a5bd529f412d959f2dbacf 100644
--- a/sumpy/expansion/__init__.py
+++ b/sumpy/expansion/__init__.py
@@ -514,7 +514,7 @@ class PDE(object):
         self.eqs = eqs
 
     def __mul__(self, param):
-        eqs = self.eqs.copy()
+        eqs = self.eqs[:]
         for eq in eqs:
             for k, v in eq.items():
                 eq[k] = eq[k] * param