diff --git a/skimage/filter/_ctmf.pyx b/skimage/filter/_ctmf.pyx
index 8133efb0..f5cd5fd0 100644
--- a/skimage/filter/_ctmf.pyx
+++ b/skimage/filter/_ctmf.pyx
@@ -18,9 +18,8 @@ from libc.stdlib cimport malloc, free
 from libc.string cimport memset
 
 cdef extern from "_histogram.h":
-    ctypedef unsigned short int uint16_t
-    void add16(uint16_t *dest, uint16_t *src)
-    void sub16(uint16_t *dest, uint16_t *src) 
+    void add16(np.uint16_t *dest, np.uint16_t *src)
+    void sub16(np.uint16_t *dest, np.uint16_t *src)
 
 np.import_array()