diff --git a/session_4/session_4.Rmd b/session_4/session_4.Rmd
index 5b0704478ccdd8d6afd3b945dd1282940f0d5dbc..7a04612cd9bb388b8a74f3f1f41c3450f6234249 100644
--- a/session_4/session_4.Rmd
+++ b/session_4/session_4.Rmd
@@ -626,7 +626,8 @@ To make the graph below, use `ggplot2`, the functions `geom_point()`, `geom_hlin
 </div> 
 
 **Tips 1 :** Don t forget the transformation of the adjusted pvalue. 
-**Tips 2 :** Feel free to search your favorite Web browser for help.
+**Tips 2 :** Feel free to search your favorite Web browser for help. 
+**Tips 3 :** `geom_label_repel()` function needs a new parameter 'data'. 
 
 ```{r VolcanoPlotDemo, echo = FALSE}
 ggplot(tab.sig, aes(x = log2FoldChange, y = -log10(padj), col = UpDown)) +