diff --git a/src/engines/ruby/2.1/Dockerfile.musl b/src/engines/ruby/2.1/Dockerfile.musl
index 72a8779..7212121 100644
--- a/src/engines/ruby/2.1/Dockerfile.musl
+++ b/src/engines/ruby/2.1/Dockerfile.musl
@@ -29,6 +29,8 @@ ARG REPRO_RUN_KEY=0
 # updated by changing the `REPRO_RUN_KEY`.
 RUN true "${REPRO_RUN_KEY}" && apk update
 
+ENV LANG en_US.UTF-8
+
 ## Install a pinned RubyGems and Bundler
 RUN gem update --system 2.7.11
 RUN gem install bundler --version 1.17.3
diff --git a/src/engines/ruby/2.2/Dockerfile.musl b/src/engines/ruby/2.2/Dockerfile.musl
index be263cd..1356c52 100644
--- a/src/engines/ruby/2.2/Dockerfile.musl
+++ b/src/engines/ruby/2.2/Dockerfile.musl
@@ -29,6 +29,8 @@ ARG REPRO_RUN_KEY=0
 # updated by changing the `REPRO_RUN_KEY`.
 RUN true "${REPRO_RUN_KEY}" && apk update
 
+ENV LANG en_US.UTF-8
+
 ## Install a pinned RubyGems and Bundler
 RUN gem update --system 2.7.11
 RUN gem install bundler --version 1.17.3
diff --git a/src/engines/ruby/2.3/Dockerfile.musl b/src/engines/ruby/2.3/Dockerfile.musl
index 0aadd04..dd8989c 100644
--- a/src/engines/ruby/2.3/Dockerfile.musl
+++ b/src/engines/ruby/2.3/Dockerfile.musl
@@ -28,6 +28,8 @@ ARG REPRO_RUN_KEY=0
 # updated by changing the `REPRO_RUN_KEY`.
 RUN true "${REPRO_RUN_KEY}" && apk update
 
+ENV LANG en_US.UTF-8
+
 ## Install a pinned RubyGems and Bundler
 RUN gem update --system 3.3.26
 RUN gem install bundler:2.3.26
diff --git a/src/engines/ruby/2.4/Dockerfile.musl b/src/engines/ruby/2.4/Dockerfile.musl
index ee2da59..aac98b8 100644
--- a/src/engines/ruby/2.4/Dockerfile.musl
+++ b/src/engines/ruby/2.4/Dockerfile.musl
@@ -28,6 +28,8 @@ ARG REPRO_RUN_KEY=0
 # updated by changing the `REPRO_RUN_KEY`.
 RUN true "${REPRO_RUN_KEY}" && apk update
 
+ENV LANG en_US.UTF-8
+
 ## Install a pinned RubyGems and Bundler
 RUN gem update --system 3.3.26
 RUN gem install bundler:2.3.26
diff --git a/src/engines/ruby/2.5/Dockerfile.musl b/src/engines/ruby/2.5/Dockerfile.musl
index 8edb08f..7021c7d 100644
--- a/src/engines/ruby/2.5/Dockerfile.musl
+++ b/src/engines/ruby/2.5/Dockerfile.musl
@@ -28,6 +28,8 @@ ARG REPRO_RUN_KEY=0
 # updated by changing the `REPRO_RUN_KEY`.
 RUN true "${REPRO_RUN_KEY}" && apk update
 
+ENV LANG en_US.UTF-8
+
 ## Install a pinned RubyGems and Bundler
 RUN gem update --system 3.3.26
 RUN gem install bundler:2.3.26
diff --git a/src/engines/ruby/2.6/Dockerfile.musl b/src/engines/ruby/2.6/Dockerfile.musl
index f5856bd..98462c3 100644
--- a/src/engines/ruby/2.6/Dockerfile.musl
+++ b/src/engines/ruby/2.6/Dockerfile.musl
@@ -28,6 +28,8 @@ ARG REPRO_RUN_KEY=0
 # updated by changing the `REPRO_RUN_KEY`.
 RUN true "${REPRO_RUN_KEY}" && apk update
 
+ENV LANG en_US.UTF-8
+
 ## Install a pinned RubyGems and Bundler
 RUN gem update --system 3.3.26
 RUN gem install bundler:2.3.26
diff --git a/src/engines/ruby/2.7/Dockerfile.musl b/src/engines/ruby/2.7/Dockerfile.musl
index 7521b59..1822987 100644
--- a/src/engines/ruby/2.7/Dockerfile.musl
+++ b/src/engines/ruby/2.7/Dockerfile.musl
@@ -28,6 +28,8 @@ ARG REPRO_RUN_KEY=0
 # updated by changing the `REPRO_RUN_KEY`.
 RUN true "${REPRO_RUN_KEY}" && apk update
 
+ENV LANG en_US.UTF-8
+
 ## Install a pinned RubyGems and Bundler
 RUN gem update --system 3.3.26
 RUN gem install bundler:2.3.26
diff --git a/src/engines/ruby/3.0/Dockerfile.musl b/src/engines/ruby/3.0/Dockerfile.musl
index 3a87a09..847fcff 100644
--- a/src/engines/ruby/3.0/Dockerfile.musl
+++ b/src/engines/ruby/3.0/Dockerfile.musl
@@ -28,6 +28,8 @@ ARG REPRO_RUN_KEY=0
 # updated by changing the `REPRO_RUN_KEY`.
 RUN true "${REPRO_RUN_KEY}" && apk update
 
+ENV LANG en_US.UTF-8
+
 ## Install a pinned RubyGems and Bundler
 RUN gem update --system 3.5.21
 RUN gem install bundler:2.3.26
diff --git a/src/engines/ruby/3.1/Dockerfile.musl b/src/engines/ruby/3.1/Dockerfile.musl
index 5f248f1..2ff39c7 100644
--- a/src/engines/ruby/3.1/Dockerfile.musl
+++ b/src/engines/ruby/3.1/Dockerfile.musl
@@ -28,6 +28,8 @@ ARG REPRO_RUN_KEY=0
 # updated by changing the `REPRO_RUN_KEY`.
 RUN true "${REPRO_RUN_KEY}" && apk update
 
+ENV LANG en_US.UTF-8
+
 ## Install a pinned RubyGems and Bundler
 RUN gem update --system 3.5.21
 RUN gem install bundler:2.3.26
diff --git a/src/engines/ruby/3.2/Dockerfile.musl b/src/engines/ruby/3.2/Dockerfile.musl
index f370a7b..98f836b 100644
--- a/src/engines/ruby/3.2/Dockerfile.musl
+++ b/src/engines/ruby/3.2/Dockerfile.musl
@@ -28,6 +28,8 @@ ARG REPRO_RUN_KEY=0
 # updated by changing the `REPRO_RUN_KEY`.
 RUN true "${REPRO_RUN_KEY}" && apk update
 
+ENV LANG en_US.UTF-8
+
 ## Install a pinned RubyGems and Bundler
 RUN gem update --system 3.5.21
 RUN gem install bundler:2.3.26
diff --git a/src/engines/ruby/3.3/Dockerfile.musl b/src/engines/ruby/3.3/Dockerfile.musl
index 9fe7520..fce5674 100644
--- a/src/engines/ruby/3.3/Dockerfile.musl
+++ b/src/engines/ruby/3.3/Dockerfile.musl
@@ -28,6 +28,8 @@ ARG REPRO_RUN_KEY=0
 # updated by changing the `REPRO_RUN_KEY`.
 RUN true "${REPRO_RUN_KEY}" && apk update
 
+ENV LANG en_US.UTF-8
+
 ## Install a pinned RubyGems and Bundler
 RUN gem update --system 3.5.21
 RUN gem install bundler:2.3.26
diff --git a/src/engines/ruby/3.4/Dockerfile.musl b/src/engines/ruby/3.4/Dockerfile.musl
index 81c4e08..592f869 100644
--- a/src/engines/ruby/3.4/Dockerfile.musl
+++ b/src/engines/ruby/3.4/Dockerfile.musl
@@ -28,6 +28,8 @@ ARG REPRO_RUN_KEY=0
 # updated by changing the `REPRO_RUN_KEY`.
 RUN true "${REPRO_RUN_KEY}" && apk update
 
+ENV LANG en_US.UTF-8
+
 ## Install a pinned RubyGems and Bundler
 RUN gem update --system 3.5.21
 RUN gem install bundler:2.3.26
diff --git a/test/engines/test_encoding.rb b/test/engines/test_encoding.rb
index bbc84e1..92ab0bf 100644
--- a/test/engines/test_encoding.rb
+++ b/test/engines/test_encoding.rb
@@ -1,13 +1,27 @@
-require 'minitest/autorun'
+require "minitest/autorun"
+
+# polyfill for Ruby 2.2 and down, used by minitest
+unless "".respond_to?(:match?)
+  String.instance_eval do
+    def match?(other)
+      (Regexp === other) ? other.match?(self) : (self == other)
+    end
+  end
+end
 
 class TestEncoding < Minitest::Test
-  def test_utf8
-    assert_equal("".encoding, Encoding::UTF_8)
+  def test_utf8_lang
+    assert_equal("en_US.UTF-8", ENV["LANG"])
+  end
+
+  def test_utf8_string
+    assert_equal(Encoding::UTF_8, "".encoding)
   end
 
   def test_read_utf8
-    contents = File.read('test/fixtures/encoding/utf-8.txt')
-    assert_equal(contents.encoding, Encoding::UTF_8)
-    assert_equal(contents, "\u2705\n")
+    contents = File.read("test/fixtures/encoding/utf-8.txt")
+
+    assert_equal(Encoding::UTF_8, contents.encoding)
+    assert_equal("\u2705\n", contents)
   end
 end