diff --git a/SimPEG/EM/FDEM/SrcFDEM.py b/SimPEG/EM/FDEM/SrcFDEM.py
index de848253..8209008c 100644
--- a/SimPEG/EM/FDEM/SrcFDEM.py
+++ b/SimPEG/EM/FDEM/SrcFDEM.py
@@ -334,7 +334,7 @@ class PrimSecSigma(BaseSrc):
     def S_eDeriv(self, prob, v, adjoint = False):
         MeSigmaDeriv = prob.MeSigmaDeriv
         if adjoint is not True:
-            return MeSigmaDeriv(Utils.mkvc(self.ePrimary)) * v # TODO: This is really sloppy and will not work if more than one freq
-        return MeSigmaDeriv(Utils.mkvc(self.ePrimary)).T * v
+            return MeSigmaDeriv(Utils.mkvc(self._ePrimary)) * v # TODO: This is really sloppy and will not work if more than one freq
+        return MeSigmaDeriv(Utils.mkvc(self._ePrimary)).T * v