diff --git a/lib/stroma/hooks/collection.rb b/lib/stroma/hooks/collection.rb
index 297df1e..1b1cdcc 100644
--- a/lib/stroma/hooks/collection.rb
+++ b/lib/stroma/hooks/collection.rb
@@ -59,7 +59,7 @@ def initialize(collection = Set.new)
       # @return [void]
       def initialize_dup(original)
         super
-        @collection = original.instance_variable_get(:@collection).dup
+        @collection = original.collection.dup
       end
 
       # Adds a new hook to the collection.
@@ -96,6 +96,10 @@ def before(key)
       def after(key)
         @collection.select { |hook| hook.after? && hook.target_key == key }
       end
+
+      protected
+
+      attr_reader :collection
     end
   end
 end
diff --git a/lib/stroma/settings/collection.rb b/lib/stroma/settings/collection.rb
index 531d4d4..8ce2bba 100644
--- a/lib/stroma/settings/collection.rb
+++ b/lib/stroma/settings/collection.rb
@@ -61,7 +61,7 @@ def initialize(storage = {})
       # @return [void]
       def initialize_dup(original)
         super
-        @storage = original.instance_variable_get(:@storage).transform_values(&:dup)
+        @storage = original.storage.transform_values(&:dup)
       end
 
       # Accesses or creates RegistrySettings for a registry key.
@@ -83,6 +83,10 @@ def [](registry_key)
       def to_h
         @storage.transform_values(&:to_h)
       end
+
+      protected
+
+      attr_reader :storage
     end
   end
 end
diff --git a/lib/stroma/settings/registry_settings.rb b/lib/stroma/settings/registry_settings.rb
index 71127ba..8e5ba8f 100644
--- a/lib/stroma/settings/registry_settings.rb
+++ b/lib/stroma/settings/registry_settings.rb
@@ -59,7 +59,7 @@ def initialize(storage = {})
       # @return [void]
       def initialize_dup(original)
         super
-        @storage = original.instance_variable_get(:@storage).transform_values(&:dup)
+        @storage = original.storage.transform_values(&:dup)
       end
 
       # Accesses or creates a Setting for an extension.
@@ -81,6 +81,10 @@ def [](extension_name)
       def to_h
         @storage.transform_values(&:to_h)
       end
+
+      protected
+
+      attr_reader :storage
     end
   end
 end
diff --git a/lib/stroma/settings/setting.rb b/lib/stroma/settings/setting.rb
index 3875b9a..a8e3449 100644
--- a/lib/stroma/settings/setting.rb
+++ b/lib/stroma/settings/setting.rb
@@ -69,7 +69,7 @@ def initialize(data = {})
       # @return [void]
       def initialize_dup(original)
         super
-        @data = deep_dup(original.instance_variable_get(:@data))
+        @data = deep_dup(original.data)
       end
 
       # Converts to a plain Hash.
@@ -93,6 +93,10 @@ def fetch(key, *args, &block)
         @data.fetch(key.to_sym, *args, &block)
       end
 
+      protected
+
+      attr_reader :data
+
       private
 
       # Recursively duplicates nested Hash and Array structures.
diff --git a/lib/stroma/state.rb b/lib/stroma/state.rb
index ad8d788..3b59301 100644
--- a/lib/stroma/state.rb
+++ b/lib/stroma/state.rb
@@ -60,8 +60,8 @@ def initialize
     # @return [void]
     def initialize_dup(original)
       super
-      @hooks = original.instance_variable_get(:@hooks).dup
-      @settings = original.instance_variable_get(:@settings).dup
+      @hooks = original.hooks.dup
+      @settings = original.settings.dup
     end
   end
 end
diff --git a/sig/lib/stroma/hooks/collection.rbs b/sig/lib/stroma/hooks/collection.rbs
index 53d8c17..733c753 100644
--- a/sig/lib/stroma/hooks/collection.rbs
+++ b/sig/lib/stroma/hooks/collection.rbs
@@ -22,6 +22,9 @@ module Stroma
       def empty?: () -> bool
 
       def size: () -> Integer
+
+      # Protected in Ruby; declared here for Steep visibility in initialize_dup
+      attr_reader collection: Set[Hook]
     end
   end
 end
diff --git a/sig/lib/stroma/settings/collection.rbs b/sig/lib/stroma/settings/collection.rbs
index fa20d7e..163f886 100644
--- a/sig/lib/stroma/settings/collection.rbs
+++ b/sig/lib/stroma/settings/collection.rbs
@@ -22,6 +22,9 @@ module Stroma
       def empty?: () -> bool
 
       def to_h: () -> Hash[Symbol, Hash[Symbol, Hash[Symbol, untyped]]]
+
+      # Protected in Ruby; declared here for Steep visibility in initialize_dup
+      attr_reader storage: Hash[Symbol, RegistrySettings]
     end
   end
 end
diff --git a/sig/lib/stroma/settings/registry_settings.rbs b/sig/lib/stroma/settings/registry_settings.rbs
index ecf2a2a..a46dc1f 100644
--- a/sig/lib/stroma/settings/registry_settings.rbs
+++ b/sig/lib/stroma/settings/registry_settings.rbs
@@ -22,6 +22,9 @@ module Stroma
       def empty?: () -> bool
 
       def to_h: () -> Hash[Symbol, Hash[Symbol, untyped]]
+
+      # Protected in Ruby; declared here for Steep visibility in initialize_dup
+      attr_reader storage: Hash[Symbol, Setting]
     end
   end
 end
diff --git a/sig/lib/stroma/settings/setting.rbs b/sig/lib/stroma/settings/setting.rbs
index 506f2dc..c4520dd 100644
--- a/sig/lib/stroma/settings/setting.rbs
+++ b/sig/lib/stroma/settings/setting.rbs
@@ -32,6 +32,9 @@ module Stroma
                | (Symbol key, untyped default) -> untyped
                | (Symbol key) { (Symbol) -> untyped } -> untyped
 
+      # Protected in Ruby; declared here for Steep visibility in initialize_dup
+      attr_reader data: Hash[Symbol, untyped]
+
       private
 
       def deep_dup: (untyped obj) -> untyped
diff --git a/spec/stroma/hooks/collection_spec.rb b/spec/stroma/hooks/collection_spec.rb
index 5356d51..6f005c8 100644
--- a/spec/stroma/hooks/collection_spec.rb
+++ b/spec/stroma/hooks/collection_spec.rb
@@ -110,4 +110,10 @@
       expect(hooks.map(&:itself)).to all(be_a(Stroma::Hooks::Hook))
     end
   end
+
+  describe "protected interface" do
+    it "does not expose collection publicly" do
+      expect { hooks.collection }.to raise_error(NoMethodError)
+    end
+  end
 end
diff --git a/spec/stroma/settings/collection_spec.rb b/spec/stroma/settings/collection_spec.rb
index c6cf432..0f92cac 100644
--- a/spec/stroma/settings/collection_spec.rb
+++ b/spec/stroma/settings/collection_spec.rb
@@ -138,4 +138,10 @@
       expect(settings[:actions][:transactional][:class]).to eq("ActiveRecord::Base")
     end
   end
+
+  describe "protected interface" do
+    it "does not expose storage publicly" do
+      expect { settings.storage }.to raise_error(NoMethodError)
+    end
+  end
 end
diff --git a/spec/stroma/settings/registry_settings_spec.rb b/spec/stroma/settings/registry_settings_spec.rb
index 6c135bf..c612d02 100644
--- a/spec/stroma/settings/registry_settings_spec.rb
+++ b/spec/stroma/settings/registry_settings_spec.rb
@@ -109,4 +109,10 @@
       expect(settings[:authorization].key?(:new_key)).to be(false)
     end
   end
+
+  describe "protected interface" do
+    it "does not expose storage publicly" do
+      expect { settings.storage }.to raise_error(NoMethodError)
+    end
+  end
 end
diff --git a/spec/stroma/settings/setting_spec.rb b/spec/stroma/settings/setting_spec.rb
index 8e8b614..1579b17 100644
--- a/spec/stroma/settings/setting_spec.rb
+++ b/spec/stroma/settings/setting_spec.rb
@@ -146,4 +146,10 @@
       expect(setting[:list][1][0]).to eq(2)
     end
   end
+
+  describe "protected interface" do
+    it "does not expose data publicly" do
+      expect { setting.data }.to raise_error(NoMethodError)
+    end
+  end
 end