diff --git a/vmm/src/api/openapi/cloud-hypervisor.yaml b/vmm/src/api/openapi/cloud-hypervisor.yaml
index aca4cc28e..34a2a668a 100644
--- a/vmm/src/api/openapi/cloud-hypervisor.yaml
+++ b/vmm/src/api/openapi/cloud-hypervisor.yaml
@@ -945,7 +945,8 @@ components:
           type: boolean
           default: false
         image_type:
-          type: enum ["FixedVhd", "Qcow2", "Raw", "Vhdx"]
+          type: string
+          enum: [FixedVhd, Qcow2, Raw, Vhdx, Unknown]
 
 
     NetConfig: