diff --git a/lib/contracted_value/core.rb b/lib/contracted_value/core.rb
index 0631699..ef03920 100644
--- a/lib/contracted_value/core.rb
+++ b/lib/contracted_value/core.rb
@@ -182,10 +182,17 @@ def extract_value(hash)
     attr_reader :default_value
 
     def raise_error_if_inputs_invalid
+      raise_error_if_name_invalid
       raise_error_if_refrigeration_mode_invalid
       raise_error_if_default_value_invalid
     end
 
+    def raise_error_if_name_invalid
+      return if name.is_a?(Symbol)
+
+      raise NotImplementedError, "Internal error: name is not a symbol (#{name.class.name})"
+    end
+
     def raise_error_if_refrigeration_mode_invalid
       return if RefrigerationMode::Enum.all.include?(refrigeration_mode)
 
@@ -231,6 +238,8 @@ def initialize(input_attr_values = {})
           )
         end
 
+      @attr_values = {}
+
       self.class.send(:attribute_set).each_attribute do |attribute|
         attr_value = attribute.extract_value(input_attr_values_hash)
 
@@ -253,8 +262,8 @@ def initialize(input_attr_values = {})
 
         # Using symbol since attribute names are limited in number
         # An alternative would be using frozen string
-        instance_variable_set(
-          :"@#{attribute.name}",
+        @attr_values.store(
+          attribute.name.to_sym,
           sometimes_frozen_attr_value,
         )
       end
@@ -265,10 +274,7 @@ def initialize(input_attr_values = {})
     # rubocop:enable Metrics/CyclomaticComplexity
 
     def to_h
-      self.class.send(:attribute_set).
-        each_attribute.each_with_object({}) do |attribute, hash|
-          hash[attribute.name] = instance_variable_get(:"@#{attribute.name}")
-        end
+      @attr_values.clone
     end
 
     # == Class interface == #
@@ -288,16 +294,19 @@ def attribute(
         refrigeration_mode: RefrigerationMode::Enum::DEEP,
         default_value: Private::ATTR_DEFAULT_VALUE_ABSENT_VAL
       )
+        # Using symbol since attribute names are limited in number
+        # An alternative would be using frozen string
+        name_in_sym = name.to_sym
 
         attr = Attribute.new(
-          name: name,
+          name: name_in_sym,
           contract: contract,
           refrigeration_mode: refrigeration_mode,
           default_value: default_value,
         )
         @attribute_set = @attribute_set.add(attr)
 
-        attr_reader(name)
+        define_method(name_in_sym) { @attr_values[name_in_sym] }
       end
 
       # @api private
diff --git a/spec/contracted_value/value_spec.rb b/spec/contracted_value/value_spec.rb
index 0673bbe..1fcaedd 100644
--- a/spec/contracted_value/value_spec.rb
+++ b/spec/contracted_value/value_spec.rb
@@ -39,6 +39,22 @@
         end
       }.to raise_error(::ContractedValue::Errors::DuplicateAttributeDeclaration)
     end
+
+    example "does not raise error when declaring 1 attribute with string name" do
+      expect {
+        value_class.class_eval do
+          attribute("attribute_1")
+        end
+      }.to_not raise_error
+    end
+
+    example "does not raise error when declaring 1 attribute with number name" do
+      expect {
+        value_class.class_eval do
+          attribute(1)
+        end
+      }.to raise_error(::NoMethodError, /undefined method `to_sym'/)
+    end
   end
 
 
@@ -93,13 +109,19 @@
 
         it "does not raise error when input is a value" do
           aggregate_failures do
+            new_val = nil
             expect {
-              value_class.new(
+              new_val = value_class.new(
                 value_class.new(
                   default_inputs,
                 ),
               )
             }.to_not raise_error
+            if new_val
+              default_inputs.each_pair do |attr_name, attr_val|
+                expect(new_val.public_send(attr_name)).to eq(attr_val)
+              end
+            end
           end
         end