diff --git a/.github/actions/fontcustom/Dockerfile b/.github/actions/fontcustom/Dockerfile
new file mode 100644
index 0000000..6ae6b39
--- /dev/null
+++ b/.github/actions/fontcustom/Dockerfile
@@ -0,0 +1,43 @@
+# Test with `docker build -t fontcustom . && docker run --rm -it fontcustom`
+FROM ruby:2.7.8-alpine
+
+# https://wiki.alpinelinux.org/wiki/GCC, including make; needed for custom builds and gem installs.
+RUN apk add --no-cache build-base
+# Needed for custom builds of sfnt2woff and woff2.
+RUN apk add --no-cache git
+
+# Workaround for
+# > Error installing fontcustom:
+# > The last version of ffi (~> 1.0) to support your Ruby & RubyGems was 1.17.0.
+# > Try installing it with `gem install ffi -v 1.17.0` and then running the current command again
+# > ffi requires RubyGems version >= 3.3.22. The current RubyGems version is 3.1.6.
+# > Try 'gem update --system' to update RubyGems itself.
+# As an additional workaround for "gem update --system" erroring with:
+# > Error installing rubygems-update:
+# > There are no versions of rubygems-update (= 3.5.14) compatible with your Ruby & RubyGems
+# > rubygems-update requires Ruby version >= 3.0.0. The current ruby version is 2.7.8.225.
+# downgrading to specific version because Rubygems 3.5 dropped support for Ruby 2.7.x
+# https://blog.rubygems.org/2023/12/15/3.5.0-released.html
+RUN gem update --system 3.4.22
+
+# Install fontcustom with all required dependencies (fontforge, python2, sfnt2woff, woff2).
+RUN gem install fontcustom --version 2.0.0
+RUN apk add --no-cache fontforge --repository=https://dl-cdn.alpinelinux.org/alpine/v3.17/community
+RUN apk add --no-cache python2   --repository=https://dl-cdn.alpinelinux.org/alpine/v3.15/community
+
+WORKDIR /tmp
+RUN git -c advice.detachedHead=false clone --branch v1.3.1 --depth 1 https://github.com/bramstein/sfnt2woff-zopfli.git \
+  && cd sfnt2woff-zopfli \
+  && make \
+  && mv sfnt2woff-zopfli sfnt2woff
+ENV PATH="$PATH:/tmp/sfnt2woff-zopfli"
+
+# Alternatively: RUN apk add --no-cache woff2
+WORKDIR /tmp
+RUN git -c advice.detachedHead=false clone --branch v1.0.2 --depth 1 --recursive https://github.com/google/woff2.git \
+  && cd woff2 \
+  && make clean all
+ENV PATH="$PATH:/tmp/woff2"
+
+COPY fontcustom.sh entrypoint.sh
+ENTRYPOINT ["/tmp/entrypoint.sh"]
diff --git a/.github/actions/fontcustom/action.yml b/.github/actions/fontcustom/action.yml
new file mode 100644
index 0000000..394c449
--- /dev/null
+++ b/.github/actions/fontcustom/action.yml
@@ -0,0 +1,15 @@
+name: "fontcustom"
+description: "Build a font from SVG files using fontcustom."
+
+inputs:
+  working-directory:
+    description: |
+      Working directory in local file system.
+      Cannot use step.*.working-directory, because it's not available with Actions only runs:.
+    required: true
+
+runs:
+  using: docker
+  image: Dockerfile
+  args:
+    - ${{ inputs.working-directory }}
diff --git a/.github/actions/fontcustom/fontcustom.sh b/.github/actions/fontcustom/fontcustom.sh
new file mode 100755
index 0000000..981b1ab
--- /dev/null
+++ b/.github/actions/fontcustom/fontcustom.sh
@@ -0,0 +1,5 @@
+#!/bin/sh -l
+set -eo pipefail
+
+cd "$1"
+fontcustom compile
diff --git a/.github/actions/iconfont/action.yml b/.github/actions/iconfont/action.yml
new file mode 100644
index 0000000..463b31d
--- /dev/null
+++ b/.github/actions/iconfont/action.yml
@@ -0,0 +1,10 @@
+name: "Build iconfont"
+description: "Build iconfont from SVG files using fontcustom."
+
+runs:
+  using: composite
+  steps:
+    - name: "Build iconfont"
+      uses: ./.github/actions/fontcustom
+      with:
+        working-directory: sources/iconfont
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 578aae6..22be7f0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -49,21 +49,8 @@ jobs:
         with:
           submodules: true
 
-      - name: "Setup old Ruby."
-        uses: ruby/setup-ruby@v1
-        with:
-          # ruby-version: sources/iconfont/.ruby-version # So checkout is needed.
-          working-directory: sources/iconfont
-          bundler-cache: false
-          cache-version: 0 # Increment this number if you need to re-download cached gems.
-
-      - name: "Install fontcustom with all dependencies."
-        working-directory: sources/iconfont
-        run: "${GITHUB_WORKSPACE}/.github/workflows/install-fontcustom.sh"
-
       - name: "Build iconfont."
-        working-directory: sources/iconfont
-        run: fontcustom compile
+        uses: ./.github/actions/iconfont
 
       - name: "Upload 'iconfont' artifact."
         uses: actions/upload-artifact@v4
@@ -164,24 +151,9 @@ jobs:
           submodules: true
           ref: ${{ steps.params.outputs.sha }}
 
-      - name: "Setup old Ruby."
-        if: ${{ steps.cache.outputs.cache-hit != 'true' }}
-        uses: ruby/setup-ruby@v1
-        with:
-          # ruby-version: sources/iconfont/.ruby-version # So checkout is needed.
-          working-directory: sources/iconfont
-          bundler-cache: false
-          cache-version: 0 # Increment this number if you need to re-download cached gems.
-
-      - name: "Install fontcustom with all dependencies."
-        if: ${{ steps.cache.outputs.cache-hit != 'true' }}
-        working-directory: sources/iconfont
-        run: "${GITHUB_WORKSPACE}/.github/workflows/install-fontcustom.sh"
-
       - name: "Build iconfont."
         if: ${{ steps.cache.outputs.cache-hit != 'true' }}
-        working-directory: sources/iconfont
-        run: fontcustom compile
+        uses: ./.github/actions/iconfont
 
       - name: "Setup Ruby."
         if: ${{ steps.cache.outputs.cache-hit != 'true' }}
diff --git a/.github/workflows/install-fontcustom.sh b/.github/workflows/install-fontcustom.sh
deleted file mode 100755
index 1314ebb..0000000
--- a/.github/workflows/install-fontcustom.sh
+++ /dev/null
@@ -1,34 +0,0 @@
-set -eo pipefail
-
-mkdir -p fontcustom && cd fontcustom
-
-# Workaround for
-# > Error installing fontcustom:
-# > The last version of ffi (~> 1.0) to support your Ruby & RubyGems was 1.17.0.
-# > Try installing it with `gem install ffi -v 1.17.0` and then running the current command again
-# > ffi requires RubyGems version >= 3.3.22. The current RubyGems version is 3.1.6.
-# > Try 'gem update --system' to update RubyGems itself.
-# As an additional workaround for "gem update --system" erroring with:
-# > Error installing rubygems-update:
-# > There are no versions of rubygems-update (= 3.5.14) compatible with your Ruby & RubyGems
-# > rubygems-update requires Ruby version >= 3.0.0. The current ruby version is 2.7.8.225.
-# downgrading to specific version because Rubygems 3.5 dropped support for Ruby 2.7.x
-# https://blog.rubygems.org/2023/12/15/3.5.0-released.html
-gem update --system 3.4.22
-
-gem install fontcustom --version 2.0.0
-
-sudo apt-get install fontforge=1:20201107~dfsg-4build1
-
-git -c advice.detachedHead=false clone --branch v1.3.1 --depth 1 https://github.com/bramstein/sfnt2woff-zopfli.git \
-  && pushd sfnt2woff-zopfli \
-  && make \
-  && mv sfnt2woff-zopfli sfnt2woff \
-  && echo "${PWD}" >> "${GITHUB_PATH}" \
-  && popd
-
-git -c advice.detachedHead=false clone --branch v1.0.2 --depth 1 --recursive https://github.com/google/woff2.git \
-  && pushd woff2 \
-  && make clean all \
-  && echo "${PWD}" >> "${GITHUB_PATH}" \
-  && popd