diff --git a/wafo/interpolate.py b/wafo/interpolate.py
index 70819e1..4e52682 100644
--- a/wafo/interpolate.py
+++ b/wafo/interpolate.py
@@ -546,7 +546,7 @@ class SmoothSpline(PPform):
             self.linear_extrapolate(output=False)
 
     def _compute_coefs(self, xx, yy, p=None, var=1):
-        x, y = np.atleast_1d(xx, yy)
+        x, y, var = np.atleast_1d(xx, yy, var)
         x = x.ravel()
         dx = np.diff(x)
         must_sort = (dx < 0).any()
@@ -573,7 +573,7 @@ class SmoothSpline(PPform):
 
         dydx = np.diff(y) / dx
 
-        if (n == 2):  # % straight line
+        if (n == 2):  # straight line
             coefs = np.vstack([dydx.ravel(), y[0, :]])
         else:
 
diff --git a/wafo/transform/estimation.py b/wafo/transform/estimation.py
index be80b9f..b365e71 100644
--- a/wafo/transform/estimation.py
+++ b/wafo/transform/estimation.py
@@ -7,7 +7,7 @@ from __future__ import absolute_import
 from .core import TrData
 from .models import TrHermite, TrOchi, TrLinear
 from ..stats import edf, skew, kurtosis
-from ..interpolate import SmoothSpline
+from ..interpolate import SmoothSpline, interp1d
 from scipy.special import ndtri as invnorm
 from scipy.integrate import cumtrapz
 import warnings
@@ -109,6 +109,7 @@ class TransformEstimator(object):
             if (dy <= 0).any():
                 dy[dy > 0] = eps
                 gvar = -(np.hstack((dy, 0)) + np.hstack((0, dy))) / 2 + eps
+                gvar = interp1d(tr.args, gvar)(tr_raw.args)
                 pp_tr = SmoothSpline(tr_raw.args, tr_raw.data, p=1,
                                      lin_extrap=self.linextrap,
                                      var=ix * gvar)