diff --git a/gnu/packages/cran.scm b/gnu/packages/cran.scm
index fb41eaf77e..f4f14031af 100644
--- a/gnu/packages/cran.scm
+++ b/gnu/packages/cran.scm
@@ -2585,6 +2585,7 @@ (define-public r-heatmaply
        ("r-ggplot2" ,r-ggplot2)
        ("r-gplots" ,r-gplots)
        ("r-htmlwidgets" ,r-htmlwidgets)
+       ("r-knitr" ,r-knitr) ; needed for vignettes
        ("r-magrittr" ,r-magrittr)
        ("r-plotly" ,r-plotly)
        ("r-rcolorbrewer" ,r-rcolorbrewer)