diff --git a/src/gaters.py b/src/gaters.py
index 96c7284718fdd05d8c3c8e0b4e873903884193cc..c3c5ef7322534807d50372a310f2ac715e01a3e9 100644
--- a/src/gaters.py
+++ b/src/gaters.py
@@ -38,7 +38,7 @@ class MahalanobisGater:
 
         """
         if meas.ndim < 2:
-            y = meas.expand_dims(meas, 0)
+            y = np.expand_dims(meas, 0)
         else:
             y = meas
         eps = y-self.sensor_model['h'](x.flatten())[:, None]