diff --git a/skimage/transform/_hough_transform.pyx b/skimage/transform/_hough_transform.pyx
index 21f6daf7..2d09751f 100644
--- a/skimage/transform/_hough_transform.pyx
+++ b/skimage/transform/_hough_transform.pyx
@@ -7,7 +7,7 @@ import numpy as np
 cimport numpy as cnp
 cimport cython
 
-from libc.math cimport abs, fabs, sqrt, ceil
+from libc.math cimport abs, fabs, sqrt, ceil, M_PI
 from libc.stdlib cimport rand
 
 from skimage.draw import circle_perimeter