diff --git a/Dockerfile b/Dockerfile
index 146edda4..eae87596 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -4,7 +4,7 @@ ENV HOME /home/stackage
 ENV LANG en_US.UTF-8
 
 # NOTE: also update debian-bootstrap.sh when cuda version changes
-ENV PATH /usr/local/cuda-8.0/bin:/opt/ghc/8.2.2/bin:/usr/sbin:/usr/bin:/sbin:/bin
+ENV PATH /usr/local/cuda-8.0/bin:/opt/ghc/8.4.1/bin:/usr/sbin:/usr/bin:/sbin:/bin
 ENV CUDA_PATH /usr/local/cuda-8.0
 ENV LD_LIBRARY_PATH=/usr/local/cuda-8.0/lib64:/usr/local/cuda-8.0/nvvm/lib64
 
diff --git a/debian-bootstrap.sh b/debian-bootstrap.sh
index 12ee32cd..cb111408 100755
--- a/debian-bootstrap.sh
+++ b/debian-bootstrap.sh
@@ -25,7 +25,7 @@ add-apt-repository -y --keyserver hkp://keyserver.ubuntu.com:80 'deb http://down
 add-apt-repository -y --keyserver hkp://keyserver.ubuntu.com:80 'deb http://download.mono-project.com/repo/debian wheezy-apache24-compat main'
 add-apt-repository -y --keyserver hkp://keyserver.ubuntu.com:80 'deb http://download.mono-project.com/repo/debian wheezy-libjpeg62-compat main'
 
-GHCVER=8.2.2
+GHCVER=8.4.1
 
 apt-get update
 apt-get install -y \
@@ -156,6 +156,12 @@ curl -sSL https://get.haskellstack.org/ | sh
 # Put documentation where we expect it
 mv /opt/ghc/$GHCVER/share/doc/ghc-$GHCVER/ /opt/ghc/$GHCVER/share/doc/ghc
 
+# llvm-5.0 for llvm-hs (separate since it needs wget)
+wget -O - http://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add - \
+    && add-apt-repository "deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-5.0 main" \
+    && apt-get update \
+    && apt-get install -y llvm-5.0
+
 # Buggy versions of ld.bfd fail to link some Haskell packages:
 # https://sourceware.org/bugzilla/show_bug.cgi?id=17689. Gold is
 # faster anyways and uses less RAM.
@@ -166,9 +172,9 @@ update-alternatives --install "/usr/bin/ld" "ld" "/usr/bin/ld.bfd" 10
 # This version is tracked here:
 # https://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/Backends/LLVM/Installing
 #
-# GHC 8.2 requires LLVM 3.9 tools (specifically, llc-3.9 and opt-3.9).
-update-alternatives --install "/usr/bin/llc" "llc" "/usr/bin/llc-3.9" 50
-update-alternatives --install "/usr/bin/opt" "opt" "/usr/bin/opt-3.9" 50
+# GHC 8.4 requires LLVM 5.0 tools (specifically, llc-5.0 and opt-5.0).
+update-alternatives --install "/usr/bin/llc" "llc" "/usr/bin/llc-5.0" 50
+update-alternatives --install "/usr/bin/opt" "opt" "/usr/bin/opt-5.0" 50
 
 # Made sure a "node" binary is in the path, as well as "nodejs".
 # A historical naming collision on Debian means that the binary is called "nodejs",
@@ -202,12 +208,6 @@ cd /tmp \
 echo "/usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/server/" > /etc/ld.so.conf.d/openjdk.conf \
     && ldconfig
 
-# llvm-4.0 for llvm-hs (separate since it needs wget)
-wget -O - http://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add - \
-    && add-apt-repository "deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-5.0 main" \
-    && apt-get update \
-    && apt-get install -y llvm-5.0
-
 # Install version 3 of the protobuf compiler.  (The `protobuf-compiler` package only
 # supports version 2.)
 curl -OL https://github.com/google/protobuf/releases/download/v3.3.0/protoc-3.3.0-linux-x86_64.zip \