diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 34a04ca4..79f7d10f 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -34,7 +34,7 @@ jobs:
           - {os: ubuntu-22.04, ruby: '3.0', db: mariadb10.6}
           - {os: ubuntu-20.04, ruby: '2.7', db: mariadb10.6}
           - {os: ubuntu-20.04, ruby: '2.7', db: mysql80}
-          - {os: ubuntu-18.04, ruby: '2.7', db: mysql57}
+          - {os: ubuntu-20.04, ruby: '2.7', db: mysql57}
 
           # TODO - Windows CI
           # - {os: windows-2022, ruby: '3.2', db: mysql80}
diff --git a/README.md b/README.md
index cf35222d..d44e77dc 100644
--- a/README.md
+++ b/README.md
@@ -107,7 +107,7 @@ Ruby runtime and MySQL client libraries are compiled with the same OpenSSL
 family, 1.0 or 1.1 or 3.0, since only one can be loaded at runtime.
 
 ``` sh
-$ brew install openssl@1.1
+$ brew install openssl@1.1 zstd
 $ gem install mysql2 -- --with-openssl-dir=$(brew --prefix openssl@1.1)
 
 or
diff --git a/ci/setup.sh b/ci/setup.sh
index 956608c6..938f0c8d 100644
--- a/ci/setup.sh
+++ b/ci/setup.sh
@@ -70,7 +70,7 @@ if [[ x$OSTYPE =~ ^xdarwin ]]; then
   done
 
   brew info "$DB"
-  brew install "$DB"
+  brew install "$DB" zstd
   DB_PREFIX="$(brew --prefix "${DB}")"
   export PATH="${DB_PREFIX}/bin:${PATH}"
   export LDFLAGS="-L${DB_PREFIX}/lib"
diff --git a/mysql2.gemspec b/mysql2.gemspec
index 93e790ae..28fd1c30 100644
--- a/mysql2.gemspec
+++ b/mysql2.gemspec
@@ -23,5 +23,5 @@ Mysql2::GEMSPEC = Gem::Specification.new do |s|
 
   s.metadata['msys2_mingw_dependencies'] = 'libmariadbclient'
 
-  s.add_runtime_dependency 'bigdecimal'
+  s.add_dependency 'bigdecimal'
 end