diff --git a/pkg/cloud/aws/actuators/machine/actuator.go b/pkg/cloud/aws/actuators/machine/actuator.go
index 8d48fc37fa..fb79a63107 100644
--- a/pkg/cloud/aws/actuators/machine/actuator.go
+++ b/pkg/cloud/aws/actuators/machine/actuator.go
@@ -306,7 +306,7 @@ func (a *Actuator) isMachineOutdated(machineSpec *v1alpha1.AWSMachineProviderSpe
 	}
 
 	// Root Device Size
-	if machineSpec.RootDeviceSize != instance.RootDeviceSize {
+	if machineSpec.RootDeviceSize > 0 && machineSpec.RootDeviceSize != instance.RootDeviceSize {
 		errs = append(errs, errors.Errorf("Root volume size cannot be mutated from %v to %v", instance.RootDeviceSize, machineSpec.RootDeviceSize))
 	}
 
diff --git a/pkg/cloud/aws/actuators/machine/actuator_test.go b/pkg/cloud/aws/actuators/machine/actuator_test.go
index a57af0d002..14aee4427b 100644
--- a/pkg/cloud/aws/actuators/machine/actuator_test.go
+++ b/pkg/cloud/aws/actuators/machine/actuator_test.go
@@ -443,6 +443,15 @@ func TestImmutableStateChange(t *testing.T) {
 			},
 			expected: 1,
 		},
+		{
+			name:        "root device size is omitted",
+			machineSpec: v1alpha1.AWSMachineProviderSpec{},
+			instance: v1alpha1.Instance{
+				// All instances have a root device size, even when we don't set one
+				RootDeviceSize: 12,
+			},
+			expected: 0,
+		},
 		{
 			name: "root device size is unchanged",
 			machineSpec: v1alpha1.AWSMachineProviderSpec{