diff --git a/CHANGELOG.md b/CHANGELOG.md
index b7a8f9d62..4fbb13c97 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,9 @@ PLEASE REMEMBER TO CHANGE THE '..main' WITH AN ACTUAL TAG in GITHUB LINK.
   commits](https://github.com/google/jax/compare/jax-v0.2.25...main).
 
 ## jaxlib 0.1.74 (Unreleased)
+* Enabled peer-to-peer copies between GPUs. Previously, GPU copies were bounced via
+  the host, which is usually slower.
+* Added experimental MLIR Python bindings for use by JAX.
 
 ## jax 0.2.25 (Nov 10, 2021)
 * [GitHub
diff --git a/jax/_src/lax/lax.py b/jax/_src/lax/lax.py
index 8881eb7ef..aa8814117 100644
--- a/jax/_src/lax/lax.py
+++ b/jax/_src/lax/lax.py
@@ -525,6 +525,8 @@ def concatenate(operands: Sequence[Array], dimension: int) -> Array:
   Returns:
     An array containing the concatenation.
   """
+  if len(operands) == 0:
+    raise ValueError("concatenate requires a non-empty sequences of arrays")
   return concatenate_p.bind(*operands, dimension=dimension)
 
 
@@ -4775,6 +4777,8 @@ def _gather_shape_rule(operand, indices, *, dimension_numbers,
 
 def _shape_as_value(shape):
   """Converts a shape that may contain Poly values into a JAX value."""
+  if len(shape) == 0:
+    return full((0,), np.array(0, np.int64))
   dims = [
       expand_dims(convert_element_type(core.dimension_as_value(d), np.int64),
                   (0,))
@@ -6605,10 +6609,10 @@ def _sort_lt_comparator(*operands, num_keys=1):
   x_keys, y_keys = [], []
   for x, y in zip(operands[:2*num_keys:2], operands[1:2*num_keys:2]):
     assert x.dtype == y.dtype, (x.dtype, y.dtype)
-    if np.issubdtype(x.dtype, np.complexfloating):
+    if dtypes.issubdtype(x.dtype, np.complexfloating):
       x_keys.extend([_float_to_int_for_sort(real(x)), _float_to_int_for_sort(imag(x))])
       y_keys.extend([_float_to_int_for_sort(real(y)), _float_to_int_for_sort(imag(y))])
-    elif np.issubdtype(x.dtype, np.floating):
+    elif dtypes.issubdtype(x.dtype, np.floating):
       x_keys.append(_float_to_int_for_sort(x))
       y_keys.append(_float_to_int_for_sort(y))
     else: