diff --git a/numcodecs/delta.py b/numcodecs/delta.py
index 9303015d..09a5601e 100644
--- a/numcodecs/delta.py
+++ b/numcodecs/delta.py
@@ -63,7 +63,8 @@ def encode(self, buf):
         enc[0] = arr[0]
 
         # compute differences
-        enc[1:] = np.diff(arr)
+        # using np.subtract for in-place operations
+        np.subtract(arr[1:], arr[0:-1], out=enc[1:])
 
         return enc