diff --git a/loopy/__init__.py b/loopy/__init__.py
index f4d47e2c7b997ea7870651e9f808659f4be692c4..30272b39ec66ae3d556f00ab8f91ef611abb8519 100644
--- a/loopy/__init__.py
+++ b/loopy/__init__.py
@@ -299,7 +299,7 @@ def cast_constraint_to_space(cns, new_space, as_equality=None):
 
 def block_shift_constraint(cns, iname, multiple, as_equality=None):
     cns = copy_constraint(cns, as_equality=as_equality)
-    cns.set_constant(cns.get_constant()
+    cns = cns.set_constant(cns.get_constant()
             + cns.get_coefficients_by_name()[iname]*multiple)
     return cns