diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index f45dd39f06..d7672e35dd 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -970,6 +970,13 @@ int libxl_device_disk_add(libxl_ctx *ctx, uint32_t domid, libxl_device_disk *dis
         goto out_free;
     }
 
+    if (disk->script) {
+        LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "External block scripts"
+                   " not yet supported, sorry");
+        rc = ERROR_INVAL;
+        goto out_free;
+    }
+
     devid = libxl__device_disk_dev_number(disk->vdev, NULL, NULL);
     if (devid==-1) {
         LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "Invalid or unsupported"
diff --git a/tools/libxl/libxl.idl b/tools/libxl/libxl.idl
index 71ad051699..b2ab52cfb1 100644
--- a/tools/libxl/libxl.idl
+++ b/tools/libxl/libxl.idl
@@ -279,6 +279,7 @@ libxl_device_disk = Struct("device_disk", [
     ("vdev", string),
     ("backend", libxl_disk_backend),
     ("format", libxl_disk_format),
+    ("script", string),
     ("unpluggable", integer),
     ("readwrite", integer),
     ("is_cdrom", integer),