diff --git a/.github/workflows/workflow.yaml b/.github/workflows/workflow.yaml
index 42923cfc..ee929bf4 100644
--- a/.github/workflows/workflow.yaml
+++ b/.github/workflows/workflow.yaml
@@ -8,9 +8,6 @@ jobs:
     steps:
       - name: Install dependencies
         run: |
-          # Use GHC 8.10.1 because of segfaults on Windows with the
-          # 8.8.* series.
-          choco install -y ghc --version 8.10.1
           choco install -y haskell-stack
           choco install -y r --version 4.0.0
       - uses: actions/checkout@v1
@@ -26,7 +23,7 @@ jobs:
             ${{ runner.os }}-stack-
       - name: Build
         run: |
-          stack build inline-r H --skip-ghc-check --system-ghc `
+          stack build inline-r H `
             --extra-lib-dirs="C:/Program files/R/R-4.0.0/bin/x64" `
             --extra-include-dirs="C:/Program files/R/R-4.0.0/include"
   test:
@@ -37,7 +34,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2
-      - uses: cachix/install-nix-action@v12
+      - uses: cachix/install-nix-action@v15
         with:
           nix_path: nixpkgs=./nixpkgs.nix
       - name: Install Stack
diff --git a/inline-r/inline-r.cabal b/inline-r/inline-r.cabal
index 44987a91..8ad1314b 100644
--- a/inline-r/inline-r.cabal
+++ b/inline-r/inline-r.cabal
@@ -88,7 +88,7 @@ library
                      , process >= 1.2
                      , reflection >= 2
                      , setenv >= 0.1.1
-                     , singletons >= 0.9
+                     , singletons >= 0.9 && < 3
                      , template-haskell >= 2.8
                      , text >= 0.11
                      , th-lift >= 0.6
diff --git a/inline-r/src/Language/R/Debug.hs b/inline-r/src/Language/R/Debug.hs
index c74cb309..061160bd 100644
--- a/inline-r/src/Language/R/Debug.hs
+++ b/inline-r/src/Language/R/Debug.hs
@@ -20,6 +20,7 @@ module Language.R.Debug
   where
 
 import Control.Memory.Region (V)
+import Data.String (fromString)
 import qualified Data.Vector.SEXP as Vector
 import qualified Foreign.R as R
 import Foreign.R (SEXP, SomeSEXP(..), SEXPTYPE, SEXPInfo)
@@ -74,7 +75,7 @@ instance ToJSON (SEXP s a) where
       miss = R.unsexp H.missingArg
       info = unsafePerformIO $ R.peekInfo x
       attr = unsafePerformIO $ R.getAttributes x
-      tp = T.pack . show $ R.infoType info
+      tp = fromString . show $ R.infoType info
       go :: SEXP s a -> Value
       go y | R.unsexp y == ub   = A.String "UnboundValue"
            | R.unsexp y == nil  = A.String "NilValue"
diff --git a/nixpkgs.nix b/nixpkgs.nix
index df02809a..dd581a69 100644
--- a/nixpkgs.nix
+++ b/nixpkgs.nix
@@ -1,7 +1,6 @@
 let
-  # 2020-12-03
-  rev = "cb52887c38ef47f6649a21336cfaa347cc7dfa75";
-  sha256 = "1i84hzcdl3fa3jl80yp7dmqx3pxaaqdiif589q10whriagvb3cp1";
+  rev = "c114cd459e1bac0d05e4e27c9ea43c99799cbbd1";
+  sha256 = "1hpspw8jbzq03k8a6izxnbqww42mihqaa6c8nszw30igiaqc98i2";
 in
 import (fetchTarball {
   inherit sha256;
diff --git a/shell.nix b/shell.nix
index 70d073df..3f2f6317 100644
--- a/shell.nix
+++ b/shell.nix
@@ -1,4 +1,4 @@
-{pkgs ? import ./nixpkgs.nix { }, ghc ? pkgs.haskell.compiler}:
+{pkgs ? import ./nixpkgs.nix { }, ghc ? pkgs.haskell.compiler.ghc8104}:
 
 with pkgs;
 
@@ -21,9 +21,9 @@ haskell.lib.buildStackProject ({
   name = "HaskellR";
   inherit ghc;
   buildInputs =
-    [ python37Packages.ipython
-      python37Packages.jupyter_client
-      python37Packages.notebook
+    [ python3Packages.ipython
+      python3Packages.jupyter_client
+      python3Packages.notebook
       R
       zeromq
       zlib
diff --git a/stack.yaml b/stack.yaml
index d1c618f0..13c33d06 100644
--- a/stack.yaml
+++ b/stack.yaml
@@ -1,4 +1,4 @@
-resolver: lts-17.1
+resolver: lts-18.6
 
 packages:
 - examples