diff --git a/skimage/filter/rank/_crank8.pyx b/skimage/filter/rank/_crank8.pyx
index d7ece4dd..c64d78ba 100644
--- a/skimage/filter/rank/_crank8.pyx
+++ b/skimage/filter/rank/_crank8.pyx
@@ -279,7 +279,7 @@ cdef inline np.uint8_t kernel_entropy(Py_ssize_t * histo, float pop,
         for i in range(256):
             p = histo[i] / pop
             if p > 0:
-                e -= p * log(p) / 0.30102999566398119521373889472449
+                e -= p * log(p) / 0.6931471805599453
 
         return < np.uint8_t > e * 10
     else: