diff --git a/properimage/propersubtract.py b/properimage/propersubtract.py
index 3dc17cc..0e6c8c3 100644
--- a/properimage/propersubtract.py
+++ b/properimage/propersubtract.py
@@ -41,7 +41,7 @@
 
 try:
     import pyfftw
-    
+
     _fftwn = pyfftw.interfaces.numpy_fft.fftn  # noqa
     _ifftwn = pyfftw.interfaces.numpy_fft.ifftn  # noqa
     print("using pyfftw interfaces API")