diff --git a/artiq/language/scan.py b/artiq/language/scan.py
index 4dd4cdd1b..e05d7aca8 100644
--- a/artiq/language/scan.py
+++ b/artiq/language/scan.py
@@ -32,7 +32,8 @@ __all__ = ["ScanObject",
 
 
 class ScanObject:
-    pass
+    def describe(self):
+        raise NotImplementedError
 
 
 class NoScan(ScanObject):