diff --git a/skimage/exposure/exposure.py b/skimage/exposure/exposure.py
index 9b1a2028..79847075 100644
--- a/skimage/exposure/exposure.py
+++ b/skimage/exposure/exposure.py
@@ -339,6 +339,7 @@ def adjust_sigmoid(image, cutoff=0.5, gain=10, inv=False):
     References
     ----------
     .. [1] http://www.cis.rit.edu/fairchild/PDFs/PAP07.pdf
+
     """
     _assert_non_negative(image)
     dtype = image.dtype.type