diff --git a/bio2zarr/vcf2zarr/icf.py b/bio2zarr/vcf2zarr/icf.py
index e0e3ea6..0559c34 100644
--- a/bio2zarr/vcf2zarr/icf.py
+++ b/bio2zarr/vcf2zarr/icf.py
@@ -1079,7 +1079,11 @@ def process_partition(self, partition_index):
                     for field in info_fields:
                         tcw.append(field.full_name, variant.INFO.get(field.name, None))
                     if has_gt:
-                        tcw.append("FORMAT/GT", variant.genotype.array())
+                        if variant.genotype is None:
+                            val = None
+                        else:
+                            val = variant.genotype.array()
+                        tcw.append("FORMAT/GT", val)
                     for field in format_fields:
                         val = variant.format(field.name)
                         tcw.append(field.full_name, val)
diff --git a/bio2zarr/vcf2zarr/vcz.py b/bio2zarr/vcf2zarr/vcz.py
index f0cd1e5..bd75320 100644
--- a/bio2zarr/vcf2zarr/vcz.py
+++ b/bio2zarr/vcf2zarr/vcz.py
@@ -321,7 +321,7 @@ def fixed_field_spec(
             array_specs.append(spec_from_field(field))
 
         if gt_field is not None:
-            ploidy = gt_field.summary.max_number - 1
+            ploidy = max(gt_field.summary.max_number - 1, 1)
             shape = [m, n]
             chunks = [variants_chunk_size, samples_chunk_size]
             dimensions = ["variants", "samples"]
@@ -728,9 +728,13 @@ def encode_genotypes_partition(self, partition_index):
         source_field = self.icf.fields["FORMAT/GT"]
         for value in source_field.iter_values(partition.start, partition.stop):
             j = gt.next_buffer_row()
-            icf.sanitise_value_int_2d(gt.buff, j, value[:, :-1])
+            icf.sanitise_value_int_2d(
+                gt.buff, j, value[:, :-1] if value is not None else None
+            )
             j = gt_phased.next_buffer_row()
-            icf.sanitise_value_int_1d(gt_phased.buff, j, value[:, -1])
+            icf.sanitise_value_int_1d(
+                gt_phased.buff, j, value[:, -1] if value is not None else None
+            )
             # TODO check is this the correct semantics when we are padding
             # with mixed ploidies?
             j = gt_mask.next_buffer_row()
diff --git a/bio2zarr/vcf2zarr/verification.py b/bio2zarr/vcf2zarr/verification.py
index a89cf8f..27e86fe 100644
--- a/bio2zarr/vcf2zarr/verification.py
+++ b/bio2zarr/vcf2zarr/verification.py
@@ -153,7 +153,7 @@ def verify(vcf_path, zarr_path, show_progress=False):
     chrom = root["contig_id"][:][root["variant_contig"][:]]
     vid = root["variant_id"][:]
     call_genotype = None
-    if "call_genotype" in root:
+    if "call_genotype" in root and root["call_genotype"].size > 0:
         call_genotype = iter(root["call_genotype"])
 
     vcf = cyvcf2.VCF(vcf_path)
diff --git a/tests/data/vcf/sample_no_genotypes_with_gt_header.vcf.gz b/tests/data/vcf/sample_no_genotypes_with_gt_header.vcf.gz
new file mode 100644
index 0000000..3029a95
Binary files /dev/null and b/tests/data/vcf/sample_no_genotypes_with_gt_header.vcf.gz differ
diff --git a/tests/data/vcf/sample_no_genotypes_with_gt_header.vcf.gz.csi b/tests/data/vcf/sample_no_genotypes_with_gt_header.vcf.gz.csi
new file mode 100644
index 0000000..9270122
Binary files /dev/null and b/tests/data/vcf/sample_no_genotypes_with_gt_header.vcf.gz.csi differ
diff --git a/tests/test_core.py b/tests/test_core.py
index 7ff33b6..74943c5 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -202,8 +202,8 @@ def test_5_chunk_1(self, n, expected):
         # It works in CI on Linux, but it'll probably break at some point.
         # It's also necessary to update these numbers each time a new data
         # file gets added
-        ("tests/data", 4973751),
-        ("tests/data/vcf", 4961614),
+        ("tests/data", 4974951),
+        ("tests/data/vcf", 4962814),
         ("tests/data/vcf/sample.vcf.gz", 1089),
     ],
 )
diff --git a/tests/test_vcf_examples.py b/tests/test_vcf_examples.py
index 4e6ac35..5b0aeeb 100644
--- a/tests/test_vcf_examples.py
+++ b/tests/test_vcf_examples.py
@@ -834,6 +834,7 @@ def test_duplicate_paths(self, tmp_path):
         "sample.vcf.gz",
         "sample_old_tabix.vcf.gz",
         "sample_no_genotypes.vcf.gz",
+        "sample_no_genotypes_with_gt_header.vcf.gz",
         "1kg_2020_chrM.vcf.gz",
         "field_type_combos.vcf.gz",
         "out_of_order_contigs.vcf.gz",