diff --git a/mvcm/ancillary.pyx b/mvcm/ancillary.pyx
index 73894f8e01623661bb08ed2952edb6273362e54b..d6c5265d844c2604398302c06435fb5492824f3d 100644
--- a/mvcm/ancillary.pyx
+++ b/mvcm/ancillary.pyx
@@ -121,7 +121,7 @@ def py_snow_mask(char *satname, unsigned char lsf):
 @cython.initializedcheck(False)
 def py_cithr(int key, np.ndarray[float, ndim=1] sec_vza, np.ndarray[float, ndim=1] bt11):
 
-    cdef np.ndarray tci_thr = np.zeros((bt11.shape[0], ), order='C', dtype=np.float)
+    cdef np.ndarray tci_thr = np.zeros((bt11.shape[0], ), order='C', dtype=np.float32)
 
     for i in range(bt11.shape[0]):
         tci_thr[i] = cithr(key, sec_vza[i], bt11[i])