diff --git a/pkg/blueprint/disk_customizations.go b/pkg/blueprint/disk_customizations.go
index 09b92099fd..4d20ca06cf 100644
--- a/pkg/blueprint/disk_customizations.go
+++ b/pkg/blueprint/disk_customizations.go
@@ -9,15 +9,37 @@ import (
 	"slices"
 	"strings"
 
+	"github.com/osbuild/images/pkg/datasizes"
 	"github.com/osbuild/images/pkg/pathpolicy"
 )
 
 type DiskCustomization struct {
 	// TODO: Add partition table type: gpt or dos
-	MinSize    uint64                   `json:"minsize,omitempty" toml:"minsize,omitempty"`
+	MinSize    uint64
+	Partitions []PartitionCustomization
+}
+
+type diskCustomizationMarshaler struct {
+	// TODO: Add partition table type: gpt or dos
+	MinSize    datasizes.Size           `json:"minsize,omitempty" toml:"minsize,omitempty"`
 	Partitions []PartitionCustomization `json:"partitions,omitempty" toml:"partitions,omitempty"`
 }
 
+func (dc *DiskCustomization) UnmarshalJSON(data []byte) error {
+	var dcm diskCustomizationMarshaler
+	if err := json.Unmarshal(data, &dcm); err != nil {
+		return err
+	}
+	dc.MinSize = dcm.MinSize.Uint64()
+	dc.Partitions = dcm.Partitions
+
+	return nil
+}
+
+func (dc *DiskCustomization) UnmarshalTOML(data any) error {
+	return unmarshalTOMLviaJSON(dc, data)
+}
+
 // PartitionCustomization defines a single partition on a disk. The Type
 // defines the kind of "payload" for the partition: plain, lvm, or btrfs.
 //   - plain: the payload will be a filesystem on a partition (e.g. xfs, ext4).
diff --git a/pkg/blueprint/disk_customizations_test.go b/pkg/blueprint/disk_customizations_test.go
index 980190015b..45a3924a93 100644
--- a/pkg/blueprint/disk_customizations_test.go
+++ b/pkg/blueprint/disk_customizations_test.go
@@ -5,10 +5,12 @@ import (
 	"testing"
 
 	"github.com/BurntSushi/toml"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
 	"github.com/osbuild/images/pkg/blueprint"
 	"github.com/osbuild/images/pkg/datasizes"
 	"github.com/osbuild/images/pkg/pathpolicy"
-	"github.com/stretchr/testify/assert"
 )
 
 func TestPartitioningValidation(t *testing.T) {
@@ -1648,3 +1650,62 @@ func TestPartitionCustomizationUnmarshalTOML(t *testing.T) {
 		})
 	}
 }
+
+func TestDiskCustomizationUnmarshalJSON(t *testing.T) {
+	type testCase struct {
+		inputJSON string
+		inputTOML string
+		expected  *blueprint.DiskCustomization
+	}
+
+	testCases := map[string]testCase{
+		"nothing": {
+			inputJSON: "{}",
+			inputTOML: "",
+			expected: &blueprint.DiskCustomization{
+				MinSize: 0,
+			},
+		},
+		"minsize/int": {
+			inputJSON: `{
+				"minsize": 1234
+			}`,
+			inputTOML: "minsize = 1234",
+			expected: &blueprint.DiskCustomization{
+				MinSize: 1234,
+			},
+		},
+		"minsize/str": {
+			inputJSON: `{
+				"minsize": "1234"
+			}`,
+			inputTOML: `minsize = "1234"`,
+			expected: &blueprint.DiskCustomization{
+				MinSize: 1234,
+			},
+		},
+		"minsize/str-with-unit": {
+			inputJSON: `{
+				"minsize": "1 GiB"
+			}`,
+			inputTOML: `minsize = "1 GiB"`,
+			expected: &blueprint.DiskCustomization{
+				MinSize: 1 * datasizes.GiB,
+			},
+		},
+	}
+
+	for name := range testCases {
+		tc := testCases[name]
+		t.Run(name, func(t *testing.T) {
+			var dc blueprint.DiskCustomization
+
+			err := json.Unmarshal([]byte(tc.inputJSON), &dc)
+			require.NoError(t, err)
+			assert.Equal(t, tc.expected, &dc)
+			err = toml.Unmarshal([]byte(tc.inputTOML), &dc)
+			require.NoError(t, err)
+			assert.Equal(t, tc.expected, &dc)
+		})
+	}
+}