diff --git a/integrators/kw1.py b/integrators/kw1.py
index 0b7ebf611fb9b08cb832a2d1a4bc6a2a81beba86..cbc86766422790ebbeec4fe12f08edb9afbad006 100644
--- a/integrators/kw1.py
+++ b/integrators/kw1.py
@@ -199,7 +199,7 @@ class KW1(_integrator._Integrator, \
 
     ### lf_iter begin
     rhs_iter_cf = -self._DerivLinearTerms_pi()
-    rhs_iter_cf = -self._DerivNonLinearTerms_Pi()
+    rhs_iter_cf -= self._DerivNonLinearTerms_Pi()
 
     self._f_iter_parts = LinearForm(self._X)
     self._f_iter_parts += SymbolicLFI(rhs_iter_cf.Compile( \