diff --git a/H/clause.h b/H/clause.h
index 6e2eacb32..a5bccf604 100644
--- a/H/clause.h
+++ b/H/clause.h
@@ -166,6 +166,7 @@ typedef struct index_t {
   PredEntry *ap;
   CELL bmap;
   int is_key;
+  UInt ncols;
   UInt hsize;
   CELL **key;
   CELL *cls;