diff --git a/simpegEM/Base.py b/simpegEM/Base.py
index 5a17c69b..690b2463 100644
--- a/simpegEM/Base.py
+++ b/simpegEM/Base.py
@@ -130,7 +130,7 @@ class BaseEMProblem(Problem.BaseProblem):
 
     # TODO: This should take a vector
     def MfRhoDeriv(self,u):
-        return self.mesh.getFaceInnerProductDeriv(self.curModel.rho)(u) * -Utils.sdiag(self.curModel.rho**2) * self.curModel.sigmaDeriv
+        return self.mesh.getFaceInnerProductDeriv(self.curModel.rho)(u) * (-Utils.sdiag(self.curModel.rho**2) * self.curModel.sigmaDeriv)
         # self.curModel.rhoDeriv
 
     @property