diff --git a/instance_disks.go b/instance_disks.go
index 176044b61..b02b32cc0 100644
--- a/instance_disks.go
+++ b/instance_disks.go
@@ -49,12 +49,13 @@ type InstanceDiskCreateOptions struct {
 	Label string `json:"label"`
 	Size  int    `json:"size"`
 
-	// Image is optional, but requires RootPass if provided
-	Image    string `json:"image,omitempty"`
-	RootPass string `json:"root_pass,omitempty"`
+	// Image is optional, but requires at least one of RootPass or AuthorizedKeys if provided
+	Image string `json:"image,omitempty"`
+
+	RootPass       string   `json:"root_pass,omitempty"`
+	AuthorizedKeys []string `json:"authorized_keys,omitempty"`
 
 	Filesystem      string            `json:"filesystem,omitempty"`
-	AuthorizedKeys  []string          `json:"authorized_keys,omitempty"`
 	AuthorizedUsers []string          `json:"authorized_users,omitempty"`
 	StackscriptID   int               `json:"stackscript_id,omitempty"`
 	StackscriptData map[string]string `json:"stackscript_data,omitempty"`
diff --git a/instances.go b/instances.go
index 31796010a..08a91ec25 100644
--- a/instances.go
+++ b/instances.go
@@ -184,16 +184,21 @@ type InstancePasswordResetOptions struct {
 
 // InstanceCreateOptions require only Region and Type
 type InstanceCreateOptions struct {
-	Region              string                   `json:"region"`
-	Type                string                   `json:"type"`
-	Label               string                   `json:"label,omitempty"`
-	RootPass            string                   `json:"root_pass,omitempty"`
-	AuthorizedKeys      []string                 `json:"authorized_keys,omitempty"`
-	AuthorizedUsers     []string                 `json:"authorized_users,omitempty"`
-	StackScriptID       int                      `json:"stackscript_id,omitempty"`
-	StackScriptData     map[string]string        `json:"stackscript_data,omitempty"`
-	BackupID            int                      `json:"backup_id,omitempty"`
-	Image               string                   `json:"image,omitempty"`
+	Region string `json:"region"`
+	Type   string `json:"type"`
+	Label  string `json:"label,omitempty"`
+
+	AuthorizedUsers []string          `json:"authorized_users,omitempty"`
+	StackScriptID   int               `json:"stackscript_id,omitempty"`
+	StackScriptData map[string]string `json:"stackscript_data,omitempty"`
+	BackupID        int               `json:"backup_id,omitempty"`
+
+	// Image is optional, but requires at least one of RootPass or AuthorizedKeys if provided
+	Image string `json:"image,omitempty"`
+
+	RootPass       string   `json:"root_pass,omitempty"`
+	AuthorizedKeys []string `json:"authorized_keys,omitempty"`
+
 	BackupsEnabled      bool                     `json:"backups_enabled,omitempty"`
 	PrivateIP           bool                     `json:"private_ip,omitempty"`
 	NetworkHelper       *bool                    `json:"network_helper,omitempty"`
@@ -226,6 +231,8 @@ type InstanceCreateOptions struct {
 	IPv4 []string `json:"ipv4,omitempty"`
 
 	MaintenancePolicy *string `json:"maintenance_policy,omitempty"`
+	Kernel            *string `json:"kernel,omitempty"`
+	BootSize          *int    `json:"boot_size,omitempty"`
 }
 
 // InstanceCreatePlacementGroupOptions represents the placement group
@@ -513,9 +520,12 @@ func (c *Client) RebootInstance(ctx context.Context, linodeID int, configID int)
 
 // InstanceRebuildOptions is a struct representing the options to send to the rebuild linode endpoint
 type InstanceRebuildOptions struct {
-	Image           string                   `json:"image,omitempty"`
-	RootPass        string                   `json:"root_pass,omitempty"`
-	AuthorizedKeys  []string                 `json:"authorized_keys,omitempty"`
+	// Image is optional, but requires at least one of RootPass or AuthorizedKeys if provided
+	Image string `json:"image,omitempty"`
+
+	RootPass       string   `json:"root_pass,omitempty"`
+	AuthorizedKeys []string `json:"authorized_keys,omitempty"`
+
 	AuthorizedUsers []string                 `json:"authorized_users,omitempty"`
 	StackScriptID   int                      `json:"stackscript_id,omitempty"`
 	StackScriptData map[string]string        `json:"stackscript_data,omitempty"`
diff --git a/test/unit/instance_disks_test.go b/test/unit/instance_disks_test.go
index d960e5471..01a9f3d19 100644
--- a/test/unit/instance_disks_test.go
+++ b/test/unit/instance_disks_test.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"testing"
 
+	"github.com/jarcoal/httpmock"
 	"github.com/linode/linodego"
 	"github.com/stretchr/testify/assert"
 )
@@ -85,9 +86,14 @@ func TestInstanceDisk_Create(t *testing.T) {
 		Label:      "New Disk",
 		Size:       20480,
 		Filesystem: "ext4",
+		RootPass:   "@S3cur3p@ssw0rd",
 	}
 
-	base.MockPost("linode/instances/123/disks", fixtureData)
+	httpmock.RegisterRegexpResponder(
+		"POST",
+		mockRequestURL(t, "/linode/instances/123/disks"),
+		mockRequestBodyValidate(t, createOptions, fixtureData),
+	)
 
 	disk, err := base.Client.CreateInstanceDisk(context.Background(), 123, createOptions)
 	assert.NoError(t, err)
diff --git a/test/unit/instance_test.go b/test/unit/instance_test.go
index f10e08d6f..26eebc2e5 100644
--- a/test/unit/instance_test.go
+++ b/test/unit/instance_test.go
@@ -180,9 +180,15 @@ func TestInstance_Create(t *testing.T) {
 		Image:             "linode/ubuntu22.04",
 		RootPass:          "securepassword",
 		MaintenancePolicy: linodego.Pointer("linode/migrate"),
+		Kernel:            linodego.Pointer("linode/6.15.7-x86_64-linode169"),
+		BootSize:          linodego.Pointer(9000),
 	}
 
-	base.MockPost("linode/instances", fixtureData)
+	httpmock.RegisterRegexpResponder(
+		"POST",
+		mockRequestURL(t, "/linode/instances"),
+		mockRequestBodyValidate(t, createOptions, fixtureData),
+	)
 
 	instance, err := base.Client.CreateInstance(context.Background(), createOptions)
 	assert.NoError(t, err)
@@ -303,10 +309,15 @@ func TestInstance_Rebuild(t *testing.T) {
 	defer base.TearDown(t)
 
 	rebuildOptions := linodego.InstanceRebuildOptions{
-		Image: "linode/ubuntu22.04",
+		RootPass: "@S3cur3p@ssw0rd",
+		Image:    "linode/ubuntu22.04",
 	}
 
-	base.MockPost("linode/instances/123/rebuild", fixtureData)
+	httpmock.RegisterRegexpResponder(
+		"POST",
+		mockRequestURL(t, "/linode/instances/123/rebuild"),
+		mockRequestBodyValidate(t, rebuildOptions, fixtureData),
+	)
 
 	instance, err := base.Client.RebuildInstance(context.Background(), 123, rebuildOptions)
 	assert.NoError(t, err)