diff --git a/src/vim9.h b/src/vim9.h
index 87ee6b1..07dd639 100644
--- a/src/vim9.h
+++ b/src/vim9.h
@@ -134,6 +134,7 @@
     // comparative operations; isn_arg.op.op_type is exprtype_T, op_ic used
     ISN_COMPAREBOOL,
     ISN_COMPARESPECIAL,
+    ISN_COMPARENULL,
     ISN_COMPARENR,
     ISN_COMPAREFLOAT,
     ISN_COMPARESTRING,