diff --git a/skimage/filter/rank/generic_cy.pyx b/skimage/filter/rank/generic_cy.pyx
index a773f62c..44c51d55 100644
--- a/skimage/filter/rank/generic_cy.pyx
+++ b/skimage/filter/rank/generic_cy.pyx
@@ -318,7 +318,7 @@ cdef inline double _kernel_otsu(Py_ssize_t* histo, double pop, dtype_t g,
     # maximizing the between class variance
     max_i = 0
     q1 = histo[0] / pop
-    m1 = 0.
+    mu1 = 0.
     max_sigma_b = 0.
 
     for i in range(1, max_bin):