diff --git a/.travis.yml b/.travis.yml
index 39f159fee..ce2782d84 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,6 +2,9 @@ language: bash
 services: docker
 
 env:
+  - VERSION=2.7-rc VARIANT=stretch
+  - VERSION=2.7-rc VARIANT=stretch/slim
+  - VERSION=2.7-rc VARIANT=alpine3.9
   - VERSION=2.6 VARIANT=stretch
   - VERSION=2.6 VARIANT=stretch/slim
   - VERSION=2.6 VARIANT=alpine3.9
diff --git a/2.7-rc/alpine3.9/Dockerfile b/2.7-rc/alpine3.9/Dockerfile
new file mode 100644
index 000000000..a1a581c75
--- /dev/null
+++ b/2.7-rc/alpine3.9/Dockerfile
@@ -0,0 +1,118 @@
+FROM alpine:3.9
+
+RUN apk add --no-cache \
+		gmp-dev
+
+# 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 2.7-rc
+ENV RUBY_VERSION 2.7.0-preview1
+ENV RUBY_DOWNLOAD_SHA256 8c546df3345398b3edc9d0ab097846f033783d33762889fd0f3dc8bb465c3354
+
+# 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
+# readline-dev vs libedit-dev: https://bugs.ruby-lang.org/issues/11869 and https://github.com/docker-library/ruby/issues/75
+RUN set -ex \
+	\
+	&& apk add --no-cache --virtual .ruby-builddeps \
+		autoconf \
+		bison \
+		bzip2 \
+		bzip2-dev \
+		ca-certificates \
+		coreutils \
+		dpkg-dev dpkg \
+		gcc \
+		gdbm-dev \
+		glib-dev \
+		libc-dev \
+		libffi-dev \
+		libxml2-dev \
+		libxslt-dev \
+		linux-headers \
+		make \
+		ncurses-dev \
+		openssl \
+		openssl-dev \
+		procps \
+		readline-dev \
+		ruby \
+		tar \
+		xz \
+		yaml-dev \
+		zlib-dev \
+	\
+	&& wget -O ruby.tar.xz "https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz" \
+	&& echo "$RUBY_DOWNLOAD_SHA256 *ruby.tar.xz" | sha256sum -c - \
+	\
+	&& mkdir -p /usr/src/ruby \
+	&& tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1 \
+	&& rm ruby.tar.xz \
+	\
+	&& cd /usr/src/ruby \
+	\
+# https://github.com/docker-library/ruby/issues/196
+# https://bugs.ruby-lang.org/issues/14387#note-13 (patch source)
+# https://bugs.ruby-lang.org/issues/14387#note-16 ("Therefore ncopa's patch looks good for me in general." -- only breaks glibc which doesn't matter here)
+	&& wget -O 'thread-stack-fix.patch' 'https://bugs.ruby-lang.org/attachments/download/7081/0001-thread_pthread.c-make-get_main_stack-portable-on-lin.patch' \
+	&& echo '3ab628a51d92fdf0d2b5835e93564857aea73e0c1de00313864a94a6255cb645 *thread-stack-fix.patch' | sha256sum -c - \
+	&& patch -p1 -i thread-stack-fix.patch \
+	&& rm thread-stack-fix.patch \
+	\
+# hack in "ENABLE_PATH_CHECK" disabling to suppress:
+#   warning: Insecure world writable dir
+	&& { \
+		echo '#define ENABLE_PATH_CHECK 0'; \
+		echo; \
+		cat file.c; \
+	} > file.c.new \
+	&& mv file.c.new file.c \
+	\
+	&& autoconf \
+	&& gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)" \
+# the configure script does not detect isnan/isinf as macros
+	&& export ac_cv_func_isnan=yes ac_cv_func_isinf=yes \
+	&& ./configure \
+		--build="$gnuArch" \
+		--disable-install-doc \
+		--enable-shared \
+	&& make -j "$(nproc)" \
+	&& make install \
+	\
+	&& runDeps="$( \
+		scanelf --needed --nobanner --format '%n#p' --recursive /usr/local \
+			| tr ',' '\n' \
+			| sort -u \
+			| awk 'system("[ -e /usr/local/lib/" $1 " ]") == 0 { next } { print "so:" $1 }' \
+	)" \
+	&& apk add --no-network --virtual .ruby-rundeps $runDeps \
+		bzip2 \
+		ca-certificates \
+		libffi-dev \
+		procps \
+		yaml-dev \
+		zlib-dev \
+	&& apk del --no-network .ruby-builddeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+# rough smoke test
+	&& ruby --version && gem --version && bundle --version
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$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/2.7-rc/stretch/Dockerfile b/2.7-rc/stretch/Dockerfile
new file mode 100644
index 000000000..196faae5a
--- /dev/null
+++ b/2.7-rc/stretch/Dockerfile
@@ -0,0 +1,73 @@
+FROM buildpack-deps:stretch
+
+# 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 2.7-rc
+ENV RUBY_VERSION 2.7.0-preview1
+ENV RUBY_DOWNLOAD_SHA256 8c546df3345398b3edc9d0ab097846f033783d33762889fd0f3dc8bb465c3354
+
+# 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 $buildDeps \
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+# rough smoke test
+	&& ruby --version && gem --version && bundle --version
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$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 "$GEM_HOME"
+# (BUNDLE_PATH = GEM_HOME, no need to mkdir/chown both)
+
+CMD [ "irb" ]
diff --git a/2.7-rc/stretch/slim/Dockerfile b/2.7-rc/stretch/slim/Dockerfile
new file mode 100644
index 000000000..6bdca75b0
--- /dev/null
+++ b/2.7-rc/stretch/slim/Dockerfile
@@ -0,0 +1,105 @@
+FROM debian:stretch-slim
+
+RUN apt-get update \
+	&& apt-get install -y --no-install-recommends \
+		bzip2 \
+		ca-certificates \
+		libffi-dev \
+		libgdbm3 \
+		libgmp-dev \
+		libssl-dev \
+		libyaml-dev \
+		procps \
+		zlib1g-dev \
+	&& rm -rf /var/lib/apt/lists/*
+
+# skip installing gem documentation
+RUN mkdir -p /usr/local/etc \
+	&& { \
+		echo 'install: --no-document'; \
+		echo 'update: --no-document'; \
+	} >> /usr/local/etc/gemrc
+
+ENV RUBY_MAJOR 2.7-rc
+ENV RUBY_VERSION 2.7.0-preview1
+ENV RUBY_DOWNLOAD_SHA256 8c546df3345398b3edc9d0ab097846f033783d33762889fd0f3dc8bb465c3354
+
+# some of ruby's build scripts are written in ruby
+#   we purge system ruby later to make sure our final image uses what we just built
+RUN set -ex \
+	\
+	&& savedAptMark="$(apt-mark showmanual)" \
+	&& apt-get update && apt-get install -y --no-install-recommends \
+		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 \
+	&& 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-mark auto '.*' > /dev/null \
+	&& apt-mark manual $savedAptMark \
+	&& find /usr/local -type f -executable -not \( -name '*tkinter*' \) -exec ldd '{}' ';' \
+		| awk '/=>/ { print $(NF-1) }' \
+		| sort -u \
+		| xargs -r dpkg-query --search \
+		| cut -d: -f1 \
+		| sort -u \
+		| xargs -r apt-mark manual \
+	&& apt-get purge -y --auto-remove -o APT::AutoRemove::RecommendsImportant=false \
+	\
+	&& cd / \
+	&& rm -r /usr/src/ruby \
+# rough smoke test
+	&& ruby --version && gem --version && bundle --version
+
+# install things globally, for great justice
+# and don't create ".bundle" in all our apps
+ENV GEM_HOME /usr/local/bundle
+ENV BUNDLE_PATH="$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 0102506f7..940360589 100755
--- a/update.sh
+++ b/update.sh
@@ -20,7 +20,8 @@ latest_gem_version() {
 # https://github.com/docker-library/ruby/issues/246
 rubygems='3.0.3'
 declare -A newEnoughRubygems=(
-	[2.6]=1 # 2.6.2 => gems 3.0.3
+	[2.6]=1 # 2.6.3 => gems 3.0.3 (https://github.com/ruby/ruby/blob/v2_6_3/lib/rubygems.rb#L12)
+	[2.7]=1 # 2.7.0-preview1 => gems 3.1.0.pre1 (https://github.com/ruby/ruby/blob/v2_7_0_preview1/lib/rubygems.rb#L12)
 )
 # TODO once all versions are in this family of "new enough", remove RUBYGEMS_VERSION code entirely
 
@@ -104,7 +105,7 @@ for version in "${versions[@]}"; do
 				;;
 		esac
 
-		if [ -n "${newEnoughRubygems[$version]:-}" ]; then
+		if [ -n "${newEnoughRubygems[$rcVersion]:-}" ]; then
 			sed -ri -e '/RUBYGEMS_VERSION/d' "$dir/Dockerfile"
 		fi