diff --git a/shell.nix b/shell.nix
index 1af57793..37d943d1 100644
--- a/shell.nix
+++ b/shell.nix
@@ -10,10 +10,10 @@ let
   R = (pkgs.R.override {enableStrictBarrier = false;}).overrideAttrs (
     # Pin R to a specific version to avoid breaking changes in the R API.
     finalAttrs: prevAttrs: {
-      version = "4.2.3";
+      version = "4.2.1";
       src = pkgs.fetchurl {
         url = "https://cran.r-project.org/src/base/R-${pkgs.lib.versions.major finalAttrs.version}/R-${finalAttrs.version}.tar.gz";
-        sha256 = "sha256-VeSpptQ74xTiwD0CZqb6VESv3OULMDv8O4Kzl5UW4HQ=";
+        sha256 = "sha256-TVLbSG0nhI5UYT1O6XetlS7AjOF4B+G1JbEM1ENsZD8=";
       };
     }
   );