diff --git a/interface-transformations/hpsMorph_function.py b/interface-transformations/hpsMorph_function.py
index e8d56b1..17514fd 100644
--- a/interface-transformations/hpsMorph_function.py
+++ b/interface-transformations/hpsMorph_function.py
@@ -1,5 +1,6 @@
 # function for doing a morph between two sounds using the hpsModel
 
+import os
 import numpy as np
 import matplotlib.pyplot as plt
 from scipy.signal import get_window
diff --git a/interface-transformations/hpsTransformations_function.py b/interface-transformations/hpsTransformations_function.py
index f30ff99..5cf9a2d 100644
--- a/interface-transformations/hpsTransformations_function.py
+++ b/interface-transformations/hpsTransformations_function.py
@@ -1,5 +1,6 @@
 # function call to the transformation functions of relevance for the hpsModel
 
+import os
 import numpy as np
 import matplotlib.pyplot as plt
 from scipy.signal import get_window
diff --git a/interface-transformations/stftMorph_function.py b/interface-transformations/stftMorph_function.py
index d73c536..4008e7b 100644
--- a/interface-transformations/stftMorph_function.py
+++ b/interface-transformations/stftMorph_function.py
@@ -1,5 +1,6 @@
 # function for doing a morph between two sounds using the stft
 
+import os
 import numpy as np
 import matplotlib.pyplot as plt
 from scipy.signal import get_window
diff --git a/interface-transformations/stochasticTransformations_function.py b/interface-transformations/stochasticTransformations_function.py
index b6520ab..7e8baa4 100644
--- a/interface-transformations/stochasticTransformations_function.py
+++ b/interface-transformations/stochasticTransformations_function.py
@@ -1,5 +1,6 @@
 # function call to the transformation function of relevance to the stochasticModel
 
+import os
 import numpy as np
 import matplotlib.pyplot as plt
 from smstools.models import stochasticModel as STC