diff --git a/guix/build-system/r.scm b/guix/build-system/r.scm
index 4daec5eb66..da06cb1358 100644
--- a/guix/build-system/r.scm
+++ b/guix/build-system/r.scm
@@ -28,7 +28,8 @@ (define-module (guix build-system r)
   #:use-module (srfi srfi-26)
   #:export (%r-build-system-modules
             r-build
-            r-build-system))
+            r-build-system
+            cran-uri))
 
 ;; Commentary:
 ;;
@@ -36,6 +37,15 @@ (define-module (guix build-system r)
 ;;
 ;; Code:
 
+(define (cran-uri name version)
+  "Return a list of URI strings for the R package archive on CRAN for the
+release corresponding to NAME and VERSION.  As only the most recent version is
+available via the first URI, the second URI points to the archived version."
+  (list (string-append "mirror://cran/src/contrib/"
+                       name "_" version ".tar.gz")
+        (string-append "mirror://cran/src/contrib/Archive/"
+                       name "/" name "_" version ".tar.gz")))
+
 (define %r-build-system-modules
   ;; Build-side modules imported by default.
   `((guix build r-build-system)