diff --git a/spacy/tokens/doc.pyx b/spacy/tokens/doc.pyx
index 511328068..8b519f1d6 100644
--- a/spacy/tokens/doc.pyx
+++ b/spacy/tokens/doc.pyx
@@ -699,8 +699,12 @@ cdef class Doc:
             # Handle inputs like doc.to_array(ORTH)
             py_attr_ids = [py_attr_ids]
         # Allow strings, e.g. 'lemma' or 'LEMMA'
-        py_attr_ids = [(IDS[id_.upper()] if hasattr(id_, "upper") else id_)
-                       for id_ in py_attr_ids]
+        py_attr_ids = [id_.upper() if hasattr(id_, "upper") else id_ for id_ in py_attr_ids]
+        for key in py_attr_ids:
+            if key not in IDS:
+                keys = [k for k in IDS.keys() if not k.startswith("FLAG")]
+                raise ValueError(Errors.E983.format(dict_name="IDS", key=key, keys=keys))
+        py_attr_ids = [IDS[id_] for id_ in py_attr_ids]
         # Make an array from the attributes --- otherwise our inner loop is
         # Python dict iteration.
         cdef np.ndarray attr_ids = numpy.asarray(py_attr_ids, dtype="i")