diff --git a/src/json.c b/src/json.c
index 8262640..dba003e 100644
--- a/src/json.c
+++ b/src/json.c
@@ -230,8 +230,7 @@
 	case VAR_PARTIAL:
 	case VAR_JOB:
 	case VAR_CHANNEL:
-	    // no JSON equivalent TODO: better error
-	    emsg(_(e_invarg));
+	    semsg(_(e_cannot_json_encode_str), vartype_name(val->v_type));
 	    return FAIL;
 
 	case VAR_BLOB: