diff --git a/Makefile b/Makefile
index 2c4b3b4..9649965 100644
--- a/Makefile
+++ b/Makefile
@@ -1,24 +1,32 @@
+R := R
+
 .PHONY: all build check document test
 
 all: document build check
 
 build: document
-	R CMD build .
+	$(R) CMD build .
 
 check: build
-	R CMD check injectr*tar.gz
+	$(R) CMD check injectr*tar.gz
 
 clean:
 	-rm -f injectr*tar.gz
 	-rm -fr injectr.Rcheck
 	-rm -fr src/*.{o,so}
 
-document: clean
-	Rscript -e 'devtools::document()'
-	Rscript -e 'rmarkdown::render("README.Rmd")'
+document: clean install-devtools install-rmarkdown
+	$(R) -s -e 'devtools::document()'
+	$(R) -s -e 'rmarkdown::render("README.Rmd")'
 
-test:
-	Rscript -e 'devtools::test()'
+test: install-devtools
+	$(R) -s -e 'devtools::test()'
 
 install: clean
-	R CMD INSTALL .
+	$(R) CMD INSTALL .
+
+install-devtools:
+	$(R) -s -e "if (!require('devtools')) install.packages('devtools', repos = 'http://cran.rstudio.com/')"
+	
+install-rmarkdown:
+	$(R) -s -e "if (!require('rmarkdown')) install.packages('rmarkdown', repos = 'http://cran.rstudio.com/')"