diff --git a/pkg/types/installconfig.go b/pkg/types/installconfig.go
index 5777e52bad2..cfb538d8bab 100644
--- a/pkg/types/installconfig.go
+++ b/pkg/types/installconfig.go
@@ -82,6 +82,11 @@ type AWSPlatform struct {
 	// UserTags specifies additional tags for AWS resources created for the cluster.
 	UserTags map[string]string `json:"userTags,omitempty"`
 
+	// DefaultMachinePlatform is the default configuration used when
+	// installing on AWS for machine pools which do not define their own
+	// platform configuration.
+	DefaultMachinePlatform *AWSMachinePoolPlatform `json:"defaultMachinePlatform,omitempty"`
+
 	// VPCID specifies the vpc to associate with the cluster.
 	// If empty, new vpc will be created.
 	// +optional
@@ -95,9 +100,16 @@ type AWSPlatform struct {
 // LibvirtPlatform stores all the global configuration that
 // all machinesets use.
 type LibvirtPlatform struct {
-	// URI
+	// URI is the identifier for the libvirtd connection.  It must be
+	// reachable from both the host (where the installer is run) and the
+	// cluster (where the cluster-API controller pod will be running).
 	URI string `json:"URI"`
 
+	// DefaultMachinePlatform is the default configuration used when
+	// installing on AWS for machine pools which do not define their own
+	// platform configuration.
+	DefaultMachinePlatform *LibvirtMachinePoolPlatform `json:"defaultMachinePlatform,omitempty"`
+
 	// Network
 	Network LibvirtNetwork `json:"network"`