diff --git a/Makefile b/Makefile
index b06646597f429e09727eac10a855cfb68d8da309..f7da904a2bec5224048ad7122f6f107219f023ae 100644
--- a/Makefile
+++ b/Makefile
@@ -62,7 +62,8 @@ motivation.html : motivation.md _layouts/slides.revealjs Makefile
 	    -o $@ $<
 
 # Pattern to convert R Markdown to Markdown.
-%.md: %.Rmd $(R_CHUNK_OPTS)
+%.md: %.Rmd $(R_CHUNK_OPTS) tools/check_knitr_version.R
+	Rscript -e "source('tools/check_knitr_version.R')"
 	Rscript -e "knitr::knit('$$(basename $<)', output = '$$(basename $@)')"
 
 ## commands : Display available commands.
diff --git a/tools/check_knitr_version.R b/tools/check_knitr_version.R
new file mode 100644
index 0000000000000000000000000000000000000000..ec6f94ce144ff3cb8434be7f907e9d655bb7f1f3
--- /dev/null
+++ b/tools/check_knitr_version.R
@@ -0,0 +1,5 @@
+if (require("knitr")) {
+    if (packageVersion("knitr") < '1.9.19') {
+        stop("knitr must be version 1.9.20 or higher")
+    }
+} else stop("knitr 1.9.20 or above is needed to build the lessons.")