diff --git a/R/plot.OutputsModel.R b/R/plot.OutputsModel.R
index a5516cc70e0e4911a1e07bb47d0e931dfb668790..e90893e844e192f2b05bcf629954209b39161eb0 100644
--- a/R/plot.OutputsModel.R
+++ b/R/plot.OutputsModel.R
@@ -19,9 +19,9 @@ plot.OutputsModel <- function(x, Qobs = NULL, IndPeriod_Plot = NULL, BasinArea =
 
   ## index time series
   if (!is.null(IndPeriod_Plot)) {
-    if (length(IndPeriod_Plot) == 0 || any(IndPeriod_Plot <= 0)) {
+    if (length(IndPeriod_Plot) <= 1 || any(IndPeriod_Plot <= 0)) {
       IndPeriod_Plot <- seq_along(OutputsModel$DatesR)
-      warning('IndPeriod_Plot')
+      stop('IndPeriod_Plot must be a positive vector of length > 0')
     }
     # IndPeriod_Plot <- seq_along(IndPeriod_Plot)
     OutputsModel <- .IndexOutputsModel(OutputsModel, IndPeriod_Plot)