diff --git a/Dockerfile b/Dockerfile
index eea0343..eee00c6 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,10 +1,11 @@
-FROM ruby:2.3.1
+FROM ruby:2.6.5
 
 ENV TEST_HOME=/pipes
 ADD *.gemspec $TEST_HOME/
 ADD Gemfile $TEST_HOME/
 WORKDIR $TEST_HOME
 
+RUN gem install bundler
 RUN bundle install --jobs 8 --retry 5
 
 ADD . $TEST_HOME
diff --git a/Gemfile b/Gemfile
index cdfab82..fa75df1 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,7 +1,3 @@
 source 'https://rubygems.org'
 
 gemspec
-
-group :test do
-  gem 'rspec'
-end
diff --git a/codequest_pipes.gemspec b/codequest_pipes.gemspec
index e312bcb..5859a35 100644
--- a/codequest_pipes.gemspec
+++ b/codequest_pipes.gemspec
@@ -14,6 +14,9 @@ Gem::Specification.new do |spec|
   spec.files      = Dir['lib/**/*.rb'] + Dir['spec/**/*.rb']
   spec.test_files = spec.files.grep(/^spec/)
 
-  spec.add_development_dependency 'bundler', '~> 1.6', '>= 1.6.9'
-  spec.add_development_dependency 'rake', '~> 10.3'
+  spec.add_development_dependency 'bundler', '~> 2.0'
+  spec.add_development_dependency 'rake', '~> 13.0'
+  spec.add_development_dependency 'rspec', '~> 3.9'
+
+  spec.add_dependency 'ice_nine', '~> 0.11'
 end
diff --git a/lib/codequest_pipes/context.rb b/lib/codequest_pipes/context.rb
index 155c1e1..fc5968c 100644
--- a/lib/codequest_pipes/context.rb
+++ b/lib/codequest_pipes/context.rb
@@ -1,3 +1,5 @@
+require 'ice_nine'
+
 require 'codequest_pipes/context/error_collector'
 
 module Pipes
@@ -16,19 +18,23 @@ class ExecutionTerminated < ::StandardError; end
     # Context constructor.
     #
     # @param values [Hash]
-    def initialize(values = {})
-      add(values)
+    def initialize(values = {}, mutable_values = {})
       @error_collector = ErrorCollector.new
+      @mutable_values = Set.new
+      add(values, mutable_values)
     end
 
     # Method `add` allows adding new properties (as a Hash) to the Context.
     #
     # @param values [Hash]
-    def add(values)
+    def add(values, mutable_values = {})
       values.each do |key, val|
-        k_sym = key.to_sym
-        fail Override, "Property :#{key} already present" if respond_to?(k_sym)
-        define_singleton_method(k_sym) { val }
+        add_value(key.to_sym, IceNine.deep_freeze(val))
+      end
+
+      mutable_values.each do |key, val|
+        add_value(key.to_sym, val)
+        @mutable_values << key
       end
     end
 
@@ -101,6 +107,13 @@ def add_errors(collectable_errors)
 
     private
 
-    attr_reader :error_collector
+    attr_reader :error_collector, :mutable_values
+
+    def add_value(key, value)
+      if respond_to?(key) && !mutable_values.include?(key)
+        fail Override, "Property :#{key} already exists and is non-mutable"
+      end
+      define_singleton_method(key) { value }
+    end
   end # class Context
 end # module Pipes
diff --git a/spec/context_spec.rb b/spec/context_spec.rb
index 0982f67..1d5edfa 100644
--- a/spec/context_spec.rb
+++ b/spec/context_spec.rb
@@ -12,6 +12,23 @@
       expect { subject.add(key: 'other_val') }
         .to raise_error(Pipes::Context::Override)
     end
+
+    it 'does not allow modifying existing fields' do
+      subject.add(key: 'val')
+      expect { subject.key << 'ue' }.to raise_error(FrozenError)
+    end
+
+    it 'allows rewriting existing mutable fields' do
+      subject.add({}, key: 'val')
+      expect { subject.add(key: 'other_val') }
+        .to change { subject.key }.from('val').to 'other_val'
+    end
+
+    it 'allows modifying existing mutable fields' do
+      subject.add({}, key: 'val')
+      expect { subject.key << 'ue' }
+        .to change { subject.key }.from('val').to 'value'
+    end
   end # describe '#add'
 
   describe '#inspect' do
diff --git a/spec/pipe_spec.rb b/spec/pipe_spec.rb
index 2dc8bb3..d644c7c 100644
--- a/spec/pipe_spec.rb
+++ b/spec/pipe_spec.rb
@@ -63,7 +63,7 @@ class RequiringNumericChild < Parent
 class NoMethodPipe < Pipes::Pipe; end
 
 describe Pipes::Pipe do
-  let(:ctx) { Pipes::Context.new(flow: []) }
+  let(:ctx) { Pipes::Context.new({}, flow: []) }
 
   subject { pipe.call(ctx) }