diff --git a/python/neuroglancer/write_annotations.py b/python/neuroglancer/write_annotations.py
index af3fa94d5..c695ec4be 100644
--- a/python/neuroglancer/write_annotations.py
+++ b/python/neuroglancer/write_annotations.py
@@ -525,7 +525,7 @@ def write(self, path: Union[str, pathlib.Path]):
             (self.upper_bound - self.lower_bound) / self.chunk_size
         ).astype(int)
 
-        np.maximum(num_chunks, np.full(num_chunks.shape, 1, dtype=int))
+        num_chunks = np.maximum(num_chunks, np.full(num_chunks.shape, 1, dtype=int))
 
         # make directories
         os.makedirs(path, exist_ok=True)