diff --git a/taskcluster/ci/build/linux.yml b/taskcluster/ci/build/linux.yml
index 69000046b0..af77168a4d 100644
--- a/taskcluster/ci/build/linux.yml
+++ b/taskcluster/ci/build/linux.yml
@@ -151,6 +151,7 @@ linux/opt:
             - linux64-binutils
             - linux64-cbindgen
             - linux64-clang
+            - linux64-clang-lib32cxx
             - linux32-libotr
             - linux64-nasm
             - linux64-node
@@ -196,6 +197,7 @@ linux-shippable/opt:
             - linux64-binutils
             - linux64-cbindgen
             - linux64-clang
+            - linux64-clang-lib32cxx
             - linux32-libotr
             - linux64-nasm
             - linux64-node
@@ -232,6 +234,7 @@ linux/debug:
             - linux64-binutils
             - linux64-cbindgen
             - linux64-clang
+            - linux64-clang-lib32cxx
             - linux64-fix-stacks  # see bug 1614626
             - linux32-libotr
             - linux64-nasm
diff --git a/taskcluster/ci/toolchain/kind.yml b/taskcluster/ci/toolchain/kind.yml
index 73d55679b0..342be8c771 100644
--- a/taskcluster/ci/toolchain/kind.yml
+++ b/taskcluster/ci/toolchain/kind.yml
@@ -73,3 +73,4 @@ transforms:
 
 jobs-from:
     - libotr.yml
+    - libcxx.yml
diff --git a/taskcluster/ci/toolchain/libcxx.yml b/taskcluster/ci/toolchain/libcxx.yml
new file mode 100644
index 0000000000..2f8fcca436
--- /dev/null
+++ b/taskcluster/ci/toolchain/libcxx.yml
@@ -0,0 +1,28 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+---
+job-defaults:
+    treeherder:
+        kind: build
+        platform: toolchains/opt
+        tier: 1
+    run-on-projects: []
+
+linux64-clang-lib32cxx:
+    description: "libc++ for linux32"
+    treeherder:
+        symbol: TL(lib32-libcxx)
+    worker-type: b-linux
+    worker:
+        max-run-time: 1800
+    run:
+        using: comm-toolchain-script
+        script: build-lib32cxx.sh
+        toolchain-artifact: public/build/lib32cxx.tar.xz
+    fetches:
+        fetch:
+            - clang-9  # Need to keep current with linux64-clang
+        toolchain:
+            - linux64-clang-9
+            - linux64-gcc-7  # Use what linux64-clang uses
diff --git a/taskcluster/scripts/build-lib32cxx.sh b/taskcluster/scripts/build-lib32cxx.sh
new file mode 100755
index 0000000000..54409bdaa9
--- /dev/null
+++ b/taskcluster/scripts/build-lib32cxx.sh
@@ -0,0 +1,89 @@
+#!/bin/bash
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+set -x -E -v
+
+# This script is for building libc++.a (linux32)
+
+# Environment variables that are set by Taskcluster.
+GECKO_PATH=${GECKO_PATH:-"/builds/worker/checkouts/gecko"}
+MOZ_FETCHES_DIR=${MOZ_FETCHES_DIR:-"/builds/worker/workspace/fetches"}
+UPLOAD_DIR=${UPLOAD_DIR:-"/builds/worker/artifacts"}
+
+cd $GECKO_PATH
+
+if [ -n "$TOOLTOOL_MANIFEST" ]; then
+  . taskcluster/scripts/misc/tooltool-download.sh
+fi
+
+if [ -d "$MOZ_FETCHES_DIR/binutils/bin" ]; then
+  export PATH="$MOZ_FETCHES_DIR/binutils/bin:$PATH"
+fi
+if [ -d "$MOZ_FETCHES_DIR/gcc/bin" ]; then
+  export PATH="$MOZ_FETCHES_DIR/gcc/bin:$PATH"
+fi
+if [ -d "$MOZ_FETCHES_DIR/clang/bin" ]; then
+  export PATH="$MOZ_FETCHES_DIR/clang/bin:$PATH"
+fi
+
+PKGDIR="${MOZ_FETCHES_DIR}/pkgdir"
+
+prepare() {
+  cd $MOZ_FETCHES_DIR/llvm-project
+  mkdir build-libcxxabi build-libcxx
+  return 0
+}
+
+build() {
+  local base_cmake_args="-G Ninja
+    -DCMAKE_BUILD_TYPE=Release
+    -DCMAKE_INSTALL_PREFIX=$PKGDIR/lib32-libc++
+    -DLLVM_LIBDIR_SUFFIX=32
+    -DLLVM_LINK_LLVM_DYLIB=ON
+    -DLLVM_ENABLE_RTTI=ON
+    -DLLVM_MAIN_SRC_DIR=$MOZ_FETCHES_DIR/llvm-project"
+
+  local abi_cmake_args="-DLIBCXXABI_INCLUDE_TESTS=OFF"
+  local cxx_cmake_args="-DPYTHON_EXECUTABLE=/usr/bin/python2.7
+    -DLIBCXX_CXX_ABI=libcxxabi
+    -DLIBCXX_CXX_ABI_INCLUDE_PATHS=${MOZ_FETCHES_DIR}/llvm-project/libcxxabi/include
+    -DLIBCXX_CXX_ABI_LIBRARY_PATH=${PKGDIR}/lib32-libc++/lib32"
+
+  cd "${MOZ_FETCHES_DIR}/llvm-project/build-libcxxabi"
+  cmake ../libcxxabi -DCMAKE_C_FLAGS:STRING="-m32 -fPIC" -DCMAKE_CXX_FLAGS:STRING="-m32 -fPIC" \
+    ${base_cmake_args} ${abi_cmake_args}
+  ninja && ninja install
+
+  cd "${MOZ_FETCHES_DIR}/llvm-project/build-libcxx"
+  cmake ../libcxx -DCMAKE_C_FLAGS:STRING="-m32 -fPIC" -DCMAKE_CXX_FLAGS:STRING="-m32 -fPIC" \
+    ${base_cmake_args} ${cxx_cmake_args}
+  ninja && ninja install
+
+  return 0
+}
+
+package() {
+  cd "${PKGDIR}"
+  mv lib32-libc++ clang # This is so when unpacked, the files overlay the clang toolchain
+  rm -rf clang/include
+
+  mkdir -p "${UPLOAD_DIR}"
+  tar cfJ "${UPLOAD_DIR}"/lib32cxx.tar.xz clang
+
+  return 0
+}
+
+# Basic dependency structure.
+# Each step depends on the previous completing successfully.
+# The packaging block depends on the build block's success.
+{
+  prepare &&
+    build &&
+    package
+} && exit 0
+
+# Ideally, the "exit 0" above ran after the packaging block ran successfully.
+# In case it didn't, error out here so CI catches it.
+exit 1