diff --git a/wafo/wave_theory/core.py b/wafo/wave_theory/core.py
index 3593d58..e844962 100644
--- a/wafo/wave_theory/core.py
+++ b/wafo/wave_theory/core.py
@@ -3,9 +3,10 @@ Created on 3. juni 2011
 
 @author: pab
 '''
+from __future__ import absolute_import
 import numpy as np
 from numpy import exp, expm1, inf, nan, pi, hstack, where, atleast_1d, cos, sin
-from dispersion_relation import w2k, k2w  # @UnusedImport
+from .dispersion_relation import w2k, k2w  # @UnusedImport
 
 __all__ = ['w2k', 'k2w', 'sensor_typeid', 'sensor_type', 'TransferFunction']