diff --git a/pkgs/development/ruby-modules/gem/default.nix b/pkgs/development/ruby-modules/gem/default.nix
index 8015fb1f6d0..347c4a79c59 100644
--- a/pkgs/development/ruby-modules/gem/default.nix
+++ b/pkgs/development/ruby-modules/gem/default.nix
@@ -181,6 +181,7 @@ stdenv.mkDerivation (attrs // {
       --force \
       --http-proxy 'http://nodtd.invalid' \
       --ignore-dependencies \
+      --install-dir "$GEM_HOME" \
       --build-root '/' \
       --backtrace \
       ${documentFlag} \