diff --git a/vignettes/ml100k.Rmd b/vignettes/ml100k.Rmd
index 93899e7..b3196b7 100644
--- a/vignettes/ml100k.Rmd
+++ b/vignettes/ml100k.Rmd
@@ -111,6 +111,7 @@ X_pmt <- apply(X,
 )
 
 colnames(X_pmt) <- paste0(colnames(X), "_permuted")
+X_pmt <- as.data.frame(X_pmt)
 ```
 
 ```{r}