diff --git a/python/zarrs/pipeline.py b/python/zarrs/pipeline.py
index 60daa7b..84d2eb3 100644
--- a/python/zarrs/pipeline.py
+++ b/python/zarrs/pipeline.py
@@ -26,14 +26,11 @@
 from .utils import (
     CollapsedDimensionError,
     DiscontiguousArrayError,
+    FillValueNoneError,
     make_chunk_info_for_rust_with_indices,
 )
 
 
-class FillValueNoneError(Exception):
-    pass
-
-
 class UnsupportedDataTypeError(Exception):
     pass
 
@@ -184,7 +181,7 @@ async def read(
         if not out.dtype.isnative:
             raise RuntimeError("Non-native byte order not supported")
         try:
-            self._raise_error_on_batch_info_error(batch_info)
+            self._raise_error_on_unsupported_batch_dtype(batch_info)
             chunks_desc = make_chunk_info_for_rust_with_indices(
                 batch_info, drop_axes, out.shape
             )
@@ -214,7 +211,7 @@ async def write(
         drop_axes: tuple[int, ...] = (),
     ) -> None:
         try:
-            self._raise_error_on_batch_info_error(batch_info)
+            self._raise_error_on_unsupported_batch_dtype(batch_info)
             chunks_desc = make_chunk_info_for_rust_with_indices(
                 batch_info, drop_axes, value.shape
             )
@@ -240,15 +237,15 @@ async def write(
             )
             return None
 
-    def _raise_error_on_batch_info_error(
+    def _raise_error_on_unsupported_batch_dtype(
         self,
         batch_info: Iterable[
             tuple[ByteSetter, ArraySpec, SelectorTuple, SelectorTuple]
         ],
     ):
         # https://github.com/LDeakin/zarrs/blob/0532fe983b7b42b59dbf84e50a2fe5e6f7bad4ce/zarrs_metadata/src/v2_to_v3.rs#L289-L293
-        if any(info.dtype.kind in {"V", "S"} for (_, info, _, _) in batch_info):
+        if any(
+            info.dtype.kind in {"V", "S", "U", "M", "m"}
+            for (_, info, _, _) in batch_info
+        ):
             raise UnsupportedDataTypeError()
-        # TODO: is there some sort of default documented somewhere?
-        if any(info.fill_value is None for (_, info, _, _) in batch_info):
-            raise FillValueNoneError()
diff --git a/python/zarrs/utils.py b/python/zarrs/utils.py
index 188d9cd..1f3331c 100644
--- a/python/zarrs/utils.py
+++ b/python/zarrs/utils.py
@@ -3,10 +3,12 @@
 import operator
 import os
 from functools import reduce
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Any
 
 import numpy as np
+from zarr.core.array_spec import ArraySpec
 from zarr.core.indexing import SelectorTuple, is_integer
+from zarr.core.metadata.v3 import DataType, parse_fill_value
 
 from zarrs._internal import Basic, WithSubset
 
@@ -15,7 +17,6 @@
     from types import EllipsisType
 
     from zarr.abc.store import ByteGetter, ByteSetter
-    from zarr.core.array_spec import ArraySpec
 
 
 # adapted from https://docs.python.org/3/library/concurrent.futures.html#concurrent.futures.ThreadPoolExecutor
@@ -31,6 +32,10 @@ class CollapsedDimensionError(Exception):
     pass
 
 
+class FillValueNoneError(Exception):
+    pass
+
+
 # This is a (mostly) copy of the function from zarr.core.indexing that fixes:
 #   DeprecationWarning: Conversion of an array with ndim > 0 to a scalar is deprecated
 # TODO: Upstream this fix
@@ -134,6 +139,24 @@ def get_shape_for_selector(
     return resulting_shape_from_index(shape, selector_tuple, drop_axes, pad=pad)
 
 
+def get_implicit_fill_value(dtype: np.dtype, fill_value: Any):
+    if fill_value is not None:
+        return fill_value
+    dtype_str = str(dtype)
+    if dtype_str == "bool":
+        fill_value = False
+    elif np.issubdtype(dtype, np.integer):
+        fill_value = 0
+    elif np.issubdtype(dtype, np.floating):
+        fill_value = 0.0
+    elif dtype_str == "object":
+        # v2 object dtype used 0 as a sentinel value for fill values to actually indicate ""
+        return 0
+    else:
+        raise FillValueNoneError()
+    return parse_fill_value(fill_value, DataType.parse(dtype))
+
+
 def make_chunk_info_for_rust_with_indices(
     batch_info: Iterable[
         tuple[ByteGetter | ByteSetter, ArraySpec, SelectorTuple, SelectorTuple]
@@ -144,6 +167,14 @@ def make_chunk_info_for_rust_with_indices(
     shape = shape if shape else (1,)  # constant array
     chunk_info_with_indices: list[WithSubset] = []
     for byte_getter, chunk_spec, chunk_selection, out_selection in batch_info:
+        if chunk_spec.fill_value is None:
+            chunk_spec = ArraySpec(
+                chunk_spec.shape,
+                chunk_spec.dtype,
+                get_implicit_fill_value(chunk_spec.dtype, chunk_spec.fill_value),
+                chunk_spec.config,
+                chunk_spec.prototype,
+            )
         chunk_info = Basic(byte_getter, chunk_spec)
         out_selection_as_slices = selector_tuple_to_slice_selection(out_selection)
         chunk_selection_as_slices = selector_tuple_to_slice_selection(chunk_selection)
@@ -168,4 +199,4 @@ def make_chunk_info_for_rust_with_indices(
                 shape=shape,
             )
         )
-    return chunk_info_with_indices
\ No newline at end of file
+    return chunk_info_with_indices
diff --git a/src/chunk_item.rs b/src/chunk_item.rs
index 8ead5fd..1d49735 100644
--- a/src/chunk_item.rs
+++ b/src/chunk_item.rs
@@ -48,6 +48,8 @@ impl Basic {
         let fill_value_bytes: Vec<u8>;
         if let Ok(fill_value_downcast) = fill_value.downcast::<PyBytes>() {
             fill_value_bytes = fill_value_downcast.as_bytes().to_vec();
+        } else if fill_value.hasattr("tobytes")? {
+            fill_value_bytes = fill_value.call_method0("tobytes")?.extract()?;
         } else if let Ok(fill_value_downcast) = fill_value.downcast::<PyInt>() {
             let fill_value_usize: usize = fill_value_downcast.extract()?;
             if fill_value_usize == (0 as usize) && dtype == "object" {
@@ -62,8 +64,6 @@ impl Basic {
                     fill_value_usize, dtype
                 )));
             }
-        } else if fill_value.hasattr("tobytes")? {
-            fill_value_bytes = fill_value.call_method0("tobytes")?.extract()?;
         } else {
             return Err(PyErr::new::<PyValueError, _>(format!(
                 "Unsupported fill value {:?}",