diff --git a/src/json.c b/src/json.c
index dba003e..25349b7 100644
--- a/src/json.c
+++ b/src/json.c
@@ -230,6 +230,7 @@
 	case VAR_PARTIAL:
 	case VAR_JOB:
 	case VAR_CHANNEL:
+	case VAR_INSTR:
 	    semsg(_(e_cannot_json_encode_str), vartype_name(val->v_type));
 	    return FAIL;