diff --git a/.travis.yml b/.travis.yml
index 5c94bc40cf..3dcfa5468b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,18 +2,26 @@ language: bash
 services: docker
 
 env:
+  - VERSION=2.6-rc VARIANT=buster
+  - VERSION=2.6-rc VARIANT=buster/slim
   - VERSION=2.6-rc VARIANT=stretch
   - VERSION=2.6-rc VARIANT=stretch/slim
   - VERSION=2.6-rc VARIANT=alpine3.7
+  - VERSION=2.5 VARIANT=buster
+  - VERSION=2.5 VARIANT=buster/slim
   - VERSION=2.5 VARIANT=stretch
   - VERSION=2.5 VARIANT=stretch/slim
   - VERSION=2.5 VARIANT=alpine3.7
+  - VERSION=2.4 VARIANT=buster
+  - VERSION=2.4 VARIANT=buster/slim
   - VERSION=2.4 VARIANT=stretch
   - VERSION=2.4 VARIANT=stretch/slim
   - VERSION=2.4 VARIANT=jessie
   - VERSION=2.4 VARIANT=jessie/slim
   - VERSION=2.4 VARIANT=alpine3.7
   - VERSION=2.4 VARIANT=alpine3.6
+  - VERSION=2.3 VARIANT=buster
+  - VERSION=2.3 VARIANT=buster/slim
   - VERSION=2.3 VARIANT=stretch
   - VERSION=2.3 VARIANT=stretch/slim
   - VERSION=2.3 VARIANT=jessie
diff --git a/2.3/buster/Dockerfile b/2.3/buster/Dockerfile
new file mode 100644
index 0000000000..b5742fd928
--- /dev/null
+++ b/2.3/buster/Dockerfile
@@ -0,0 +1,79 @@
+FROM buildpack-deps:buster
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.3
+ENV RUBY_VERSION 2.3.7
+ENV RUBY_DOWNLOAD_SHA256 c61f8f2b9d3ffff5567e186421fa191f0d5e7c2b189b426bb84498825d548edb
+ENV RUBYGEMS_VERSION 2.7.7
+ENV BUNDLER_VERSION 1.16.3
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		bison \
+		dpkg-dev \
+		libgdbm-dev \
+		# ruby 2.3 on stretch can only support libssl1.0-dev (libssl dev from buildpack-deps is 1.1.x)
+		libssl1.0-dev \
+		ruby \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/2.3/buster/slim/Dockerfile b/2.3/buster/slim/Dockerfile
new file mode 100644
index 0000000000..5c8f3cea19
--- /dev/null
+++ b/2.3/buster/slim/Dockerfile
@@ -0,0 +1,104 @@
+FROM debian:buster
+
+RUN apt-get update \
+	&& apt-get install -y --no-install-recommends \
+		bzip2 \
+		ca-certificates \
+		libffi-dev \
+		libgdbm5 \
+		libgdbm-compat-dev \
+		libssl1.0-dev \
+		libyaml-dev \
+		procps \
+		zlib1g-dev \
+	&& rm -rf /var/lib/apt/lists/*
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.3
+ENV RUBY_VERSION 2.3.7
+ENV RUBY_DOWNLOAD_SHA256 c61f8f2b9d3ffff5567e186421fa191f0d5e7c2b189b426bb84498825d548edb
+ENV RUBYGEMS_VERSION 2.7.7
+ENV BUNDLER_VERSION 1.16.3
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		autoconf \
+		bison \
+		dpkg-dev \
+		gcc \
+		libbz2-dev \
+		libgdbm-dev \
+		libglib2.0-dev \
+		libncurses-dev \
+		libreadline-dev \
+		libxml2-dev \
+		libxslt-dev \
+		make \
+		ruby \
+		wget \
+		xz-utils \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& dpkg-query --show --showformat '${package}\n' \
+		| grep -P '^libreadline\d+$' \
+		| xargs apt-mark manual \
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/2.4/buster/Dockerfile b/2.4/buster/Dockerfile
new file mode 100644
index 0000000000..9afc12bb74
--- /dev/null
+++ b/2.4/buster/Dockerfile
@@ -0,0 +1,77 @@
+FROM buildpack-deps:buster
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.4
+ENV RUBY_VERSION 2.4.4
+ENV RUBY_DOWNLOAD_SHA256 1d0034071d675193ca769f64c91827e5f54cb3a7962316a41d5217c7bc6949f0
+ENV RUBYGEMS_VERSION 2.7.7
+ENV BUNDLER_VERSION 1.16.3
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		bison \
+		dpkg-dev \
+		libgdbm-dev \
+		ruby \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/2.4/buster/slim/Dockerfile b/2.4/buster/slim/Dockerfile
new file mode 100644
index 0000000000..bf5c37398a
--- /dev/null
+++ b/2.4/buster/slim/Dockerfile
@@ -0,0 +1,104 @@
+FROM debian:buster
+
+RUN apt-get update \
+	&& apt-get install -y --no-install-recommends \
+		bzip2 \
+		ca-certificates \
+		libffi-dev \
+		libgdbm5 \
+		libgdbm-compat-dev \
+		libssl-dev \
+		libyaml-dev \
+		procps \
+		zlib1g-dev \
+	&& rm -rf /var/lib/apt/lists/*
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.4
+ENV RUBY_VERSION 2.4.4
+ENV RUBY_DOWNLOAD_SHA256 1d0034071d675193ca769f64c91827e5f54cb3a7962316a41d5217c7bc6949f0
+ENV RUBYGEMS_VERSION 2.7.7
+ENV BUNDLER_VERSION 1.16.3
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		autoconf \
+		bison \
+		dpkg-dev \
+		gcc \
+		libbz2-dev \
+		libgdbm-dev \
+		libglib2.0-dev \
+		libncurses-dev \
+		libreadline-dev \
+		libxml2-dev \
+		libxslt-dev \
+		make \
+		ruby \
+		wget \
+		xz-utils \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& dpkg-query --show --showformat '${package}\n' \
+		| grep -P '^libreadline\d+$' \
+		| xargs apt-mark manual \
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/2.5/buster/Dockerfile b/2.5/buster/Dockerfile
new file mode 100644
index 0000000000..83545000e9
--- /dev/null
+++ b/2.5/buster/Dockerfile
@@ -0,0 +1,77 @@
+FROM buildpack-deps:buster
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.5
+ENV RUBY_VERSION 2.5.1
+ENV RUBY_DOWNLOAD_SHA256 886ac5eed41e3b5fc699be837b0087a6a5a3d10f464087560d2d21b3e71b754d
+ENV RUBYGEMS_VERSION 2.7.7
+ENV BUNDLER_VERSION 1.16.3
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		bison \
+		dpkg-dev \
+		libgdbm-dev \
+		ruby \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/2.5/buster/slim/Dockerfile b/2.5/buster/slim/Dockerfile
new file mode 100644
index 0000000000..71c5a343da
--- /dev/null
+++ b/2.5/buster/slim/Dockerfile
@@ -0,0 +1,104 @@
+FROM debian:buster
+
+RUN apt-get update \
+	&& apt-get install -y --no-install-recommends \
+		bzip2 \
+		ca-certificates \
+		libffi-dev \
+		libgdbm5 \
+		libgdbm-compat-dev \
+		libssl-dev \
+		libyaml-dev \
+		procps \
+		zlib1g-dev \
+	&& rm -rf /var/lib/apt/lists/*
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.5
+ENV RUBY_VERSION 2.5.1
+ENV RUBY_DOWNLOAD_SHA256 886ac5eed41e3b5fc699be837b0087a6a5a3d10f464087560d2d21b3e71b754d
+ENV RUBYGEMS_VERSION 2.7.7
+ENV BUNDLER_VERSION 1.16.3
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		autoconf \
+		bison \
+		dpkg-dev \
+		gcc \
+		libbz2-dev \
+		libgdbm-dev \
+		libglib2.0-dev \
+		libncurses-dev \
+		libreadline-dev \
+		libxml2-dev \
+		libxslt-dev \
+		make \
+		ruby \
+		wget \
+		xz-utils \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& dpkg-query --show --showformat '${package}\n' \
+		| grep -P '^libreadline\d+$' \
+		| xargs apt-mark manual \
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/2.6-rc/buster/Dockerfile b/2.6-rc/buster/Dockerfile
new file mode 100644
index 0000000000..5fcda0e71d
--- /dev/null
+++ b/2.6-rc/buster/Dockerfile
@@ -0,0 +1,77 @@
+FROM buildpack-deps:buster
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.6-rc
+ENV RUBY_VERSION 2.6.0-preview2
+ENV RUBY_DOWNLOAD_SHA256 00ddfb5e33dee24469dd0b203597f7ecee66522ebb496f620f5815372ea2d3ec
+ENV RUBYGEMS_VERSION 2.7.7
+ENV BUNDLER_VERSION 1.16.3
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		bison \
+		dpkg-dev \
+		libgdbm-dev \
+		ruby \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/2.6-rc/buster/slim/Dockerfile b/2.6-rc/buster/slim/Dockerfile
new file mode 100644
index 0000000000..2c5560b6c0
--- /dev/null
+++ b/2.6-rc/buster/slim/Dockerfile
@@ -0,0 +1,104 @@
+FROM debian:buster
+
+RUN apt-get update \
+	&& apt-get install -y --no-install-recommends \
+		bzip2 \
+		ca-certificates \
+		libffi-dev \
+		libgdbm5 \
+		libgdbm-compat-dev \
+		libssl-dev \
+		libyaml-dev \
+		procps \
+		zlib1g-dev \
+	&& rm -rf /var/lib/apt/lists/*
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.6-rc
+ENV RUBY_VERSION 2.6.0-preview2
+ENV RUBY_DOWNLOAD_SHA256 00ddfb5e33dee24469dd0b203597f7ecee66522ebb496f620f5815372ea2d3ec
+ENV RUBYGEMS_VERSION 2.7.7
+ENV BUNDLER_VERSION 1.16.3
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& buildDeps=' \
+		autoconf \
+		bison \
+		dpkg-dev \
+		gcc \
+		libbz2-dev \
+		libgdbm-dev \
+		libglib2.0-dev \
+		libncurses-dev \
+		libreadline-dev \
+		libxml2-dev \
+		libxslt-dev \
+		make \
+		ruby \
+		wget \
+		xz-utils \
+	' \
+	&& apt-get update \
+	&& apt-get install -y --no-install-recommends $buildDeps \
+	&& rm -rf /var/lib/apt/lists/* \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& dpkg-query --show --showformat '${package}\n' \
+		| grep -P '^libreadline\d+$' \
+		| xargs apt-mark manual \
+	&& apt-get purge -y --auto-remove $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+	\
+	&& gem update --system "$RUBYGEMS_VERSION" \
+	&& gem install bundler --version "$BUNDLER_VERSION" --force \
+	&& rm -r /root/.gem/
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$GEM_HOME" \
+	BUNDLE_SILENCE_ROOT_WARNING=1 \
+	BUNDLE_APP_CONFIG="$GEM_HOME"
+# path recommendation: https://github.com/bundler/bundler/pull/6469#issuecomment-383235438
+ENV PATH $GEM_HOME/bin:$BUNDLE_PATH/gems/bin:$PATH
+# adjust permissions of a few directories for running "gem install" as an arbitrary user
+RUN mkdir -p "$GEM_HOME" && chmod 777 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/update.sh b/update.sh
index a55320b566..510ae29394 100755
--- a/update.sh
+++ b/update.sh
@@ -67,7 +67,7 @@ for version in "${versions[@]}"; do
 
 	for v in \
 		alpine{3.6,3.7} \
-		{jessie,stretch}{/slim,} \
+		{jessie,stretch,buster}{/slim,} \
 	; do
 		dir="$version/$v"
 		variant="$(basename "$v")"