diff --git a/src/basic/os-util.c b/src/basic/os-util.c
index 619a2bae96..35c7555461 100644
--- a/src/basic/os-util.c
+++ b/src/basic/os-util.c
@@ -156,6 +156,9 @@ int open_extension_release(
         if (!extension)
                 return open_os_release(root, ret_path, ret_fd);
 
+        if (!IN_SET(image_class, IMAGE_SYSEXT, IMAGE_CONFEXT))
+                return -EINVAL;
+
         const char *extension_full_path;
 
         if (!image_name_is_valid(extension))