diff --git a/spacy/attrs.pxd b/spacy/attrs.pxd
index d2ace1cff..c810762ef 100644
--- a/spacy/attrs.pxd
+++ b/spacy/attrs.pxd
@@ -84,3 +84,4 @@ cpdef enum attr_id_t:
     ENT_TYPE
     HEAD
     SPACY
+    PROB