diff --git a/nipype/interfaces/cmtk/convert.py b/nipype/interfaces/cmtk/convert.py
index 4f55242a94..a17ccece6d 100644
--- a/nipype/interfaces/cmtk/convert.py
+++ b/nipype/interfaces/cmtk/convert.py
@@ -194,7 +194,7 @@ def _run_interface(self, runtime):
             for data in self.inputs.data_files:
                 _, data_name, _ = split_filename(data)
                 cda = cf.CData(name=data_name, src=data, fileformat="NumPy")
-                if string.find(data_name, 'lengths') != -1:
+                if 'lengths' in data_name:
                     cda.dtype = "FinalFiberLengthArray"
                 if string.find(data_name, 'endpoints') != -1:
                     cda.dtype = "FiberEndpoints"