diff --git a/bio2zarr/vcf.py b/bio2zarr/vcf.py
index 31b17bc..9665325 100644
--- a/bio2zarr/vcf.py
+++ b/bio2zarr/vcf.py
@@ -1068,14 +1068,16 @@ def iter_alleles_and_genotypes(self, start, stop, shape, num_alleles):
             for variant_length, alleles in zip(
                 variant_lengths, self.iter_alleles(start, stop, num_alleles)
             ):
-                yield vcz.VariantData(variant_length, alleles, None, None)
+                # Stored ICF values are always at least 1D arrays; "rlen" is Number=1
+                # so we must extract the scalar to avoid NumPy scalar-conversion issues.
+                yield vcz.VariantData(variant_length[0], alleles, None, None)
         else:
             for variant_length, alleles, (gt, phased) in zip(
                 variant_lengths,
                 self.iter_alleles(start, stop, num_alleles),
                 self.iter_genotypes(shape, start, stop),
             ):
-                yield vcz.VariantData(variant_length, alleles, gt, phased)
+                yield vcz.VariantData(variant_length[0], alleles, gt, phased)
 
     def generate_schema(
         self, variants_chunk_size=None, samples_chunk_size=None, local_alleles=None
diff --git a/docs/Makefile b/docs/Makefile
index a295590..732920e 100644
--- a/docs/Makefile
+++ b/docs/Makefile
@@ -9,6 +9,7 @@ B2Z_VERSION:=$(shell PYTHONPATH=${PYPATH} \
 CASTS=_static/vcf2zarr_convert.cast\
 	_static/vcf2zarr_explode.cast
 
+ASCIINEMA_ARGS=-c "env PS1=\\$$\\  bash --noprofile --norc"
 
 BUILDDIR      = _build
 
@@ -36,7 +37,7 @@ sample.vcf.gz:
 
 _static/vcf2zarr_convert.cast: sample.vcf.gz
 	rm -fR sample.vcz
-	asciinema-automation -d cast_scripts/vcf2zarr_convert.sh $@
+	asciinema-automation -aa '$(ASCIINEMA_ARGS)' -d cast_scripts/vcf2zarr_convert.sh $@
 	cat _static/vcf2zarr_convert.log
 	asciinema play _static/vcf2zarr_convert.cast 
 	cp -R sample.vcz vcf2zarr
@@ -44,7 +45,7 @@ _static/vcf2zarr_convert.cast: sample.vcf.gz
 # TODO rename this cast
 _static/vcf2zarr_explode.cast: sample.vcf.gz
 	rm -Rf sample.icf sample.vcz
-	asciinema-automation -d cast_scripts/vcf2zarr_explode.sh $@
+	asciinema-automation -aa '$(ASCIINEMA_ARGS)' -d cast_scripts/vcf2zarr_explode.sh $@
 	cat _static/vcf2zarr_explode.log
 	asciinema play _static/vcf2zarr_explode.cast 
 	cp -R sample.icf sample.vcz vcf2zarr
diff --git a/docs/build.sh b/docs/build.sh
index 4165d36..b91b52f 100755
--- a/docs/build.sh
+++ b/docs/build.sh
@@ -1,4 +1,4 @@
-#/bin/bash
+#!/usr/bin/env bash
 
 # Jupyter-build doesn't have an option to automatically show the 
 # saved reports, which makes it difficult to debug the reasons for 
@@ -6,7 +6,7 @@
 
 REPORTDIR=_build/html/reports
 
-jupyter-book build -Wn --keep-going .
+jupyter-book build -W -n --keep-going .
 RETVAL=$?
 if [ $RETVAL -ne 0 ]; then
     if [ -e $REPORTDIR ]; then
diff --git a/docs/requirements.txt b/docs/requirements.txt
index 8a466d7..948df41 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1,4 +1,4 @@
 asciinema-automation
 bash_kernel
-jupyter-book
+jupyter-book<2
 sphinx-click
diff --git a/docs/vcf2zarr/tutorial.md b/docs/vcf2zarr/tutorial.md
index 2125096..42817e3 100644
--- a/docs/vcf2zarr/tutorial.md
+++ b/docs/vcf2zarr/tutorial.md
@@ -62,7 +62,7 @@ of these arrays is then stored hierarchically within
 these directories:
 
 ```{code-cell}
-tree sample.vcz
+find sample.vcz -maxdepth 2 -type d | sort
 ```
 
 You can get a better idea of what's being stored and the sizes
diff --git a/pyproject.toml b/pyproject.toml
index 50e52f2..98d9fd0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -65,14 +65,14 @@ dev = [
   "pytest-xdist",
   "sgkit>=0.8.0",
   "tqdm",
-  "tskit>=0.6.4",
+  "tskit>=0.6.4,<1",
   "bed_reader",
   "cyvcf2"
 ]
-tskit = ["tskit>=0.6.4"]
+tskit = ["tskit>=0.6.4,<1"]
 vcf = ["cyvcf2"]
 all = [
-  "tskit>=0.6.4", 
+  "tskit>=0.6.4,<1",
   "cyvcf2"
 ]