diff --git a/spectral_cube/cube_utils.py b/spectral_cube/cube_utils.py
index 6e7c40a59..cc991e5e4 100644
--- a/spectral_cube/cube_utils.py
+++ b/spectral_cube/cube_utils.py
@@ -972,8 +972,8 @@ def log_(x):
         output_footprint = np.memmap(ntf2, mode='w+', shape=shape_opt, dtype=dtype)
     else:
         log_("Using memory")
-        output_array = np.zeros(shape_opt)
-        output_footprint = np.zeros(shape_opt)
+        output_array = np.zeros(shape_opt, dtype=dtype)
+        output_footprint = np.zeros(shape_opt, dtype=dtype)
     mask_opt = np.zeros(shape_opt[1:])