diff --git a/lib/jsonb_accessor/macro.rb b/lib/jsonb_accessor/macro.rb
index 03e25e7..63c309f 100644
--- a/lib/jsonb_accessor/macro.rb
+++ b/lib/jsonb_accessor/macro.rb
@@ -91,9 +91,8 @@ def jsonb_accessor(jsonb_attribute, field_types)
 
             empty_named_attributes = names_to_store_keys.transform_values { nil }
             empty_named_attributes.merge(value_with_named_keys).each do |name, attribute_value|
-              # Undefined keys: There might be things in the JSON that haven't been defined using jsonb_accessor
-              # It should still be possible to save arbitrary data in the JSON
-              next unless has_attribute? name
+              # Only proceed if this attribute has been defined using `jsonb_accessor`.
+              next unless names_to_store_keys.key?(name)
 
               write_attribute(name, attribute_value)
             end
diff --git a/spec/jsonb_accessor_spec.rb b/spec/jsonb_accessor_spec.rb
index 975c5f1..7d05346 100644
--- a/spec/jsonb_accessor_spec.rb
+++ b/spec/jsonb_accessor_spec.rb
@@ -8,6 +8,8 @@ def build_class(jsonb_accessor_config, &block)
       self.table_name = "products"
       jsonb_accessor :options, jsonb_accessor_config
       instance_eval(&block) if block
+
+      attribute :bang, :string
     end
   end
 
@@ -274,6 +276,12 @@ def build_class(jsonb_accessor_config, &block)
         expect(subklass_instance.sub).to be_nil
       end
     end
+
+    it "does not write a normal Ruby attribute" do
+      expect(instance.bang).to be_nil
+      instance.options = { bang: "bang" }
+      expect(instance.bang).to be_nil
+    end
   end
 
   context "dirty tracking for already persisted models" do