diff --git a/lib/apipie-rails.rb b/lib/apipie-rails.rb
index 5e647fc28..27ea554ad 100644
--- a/lib/apipie-rails.rb
+++ b/lib/apipie-rails.rb
@@ -27,3 +27,5 @@
 require "apipie/generator/swagger/swagger"
 require "apipie/generator/swagger/warning"
 require "apipie/generator/swagger/warning_writer"
+require "apipie/generator/swagger/type"
+require "apipie/generator/swagger/type_extractor"
diff --git a/lib/apipie/generator/generator.rb b/lib/apipie/generator/generator.rb
new file mode 100644
index 000000000..548157f34
--- /dev/null
+++ b/lib/apipie/generator/generator.rb
@@ -0,0 +1,2 @@
+module Apipie::Generator
+end
diff --git a/lib/apipie/generator/swagger/swagger.rb b/lib/apipie/generator/swagger/swagger.rb
new file mode 100644
index 000000000..b4b64ad57
--- /dev/null
+++ b/lib/apipie/generator/swagger/swagger.rb
@@ -0,0 +1,2 @@
+module Apipie::Generator::Swagger
+end
diff --git a/lib/apipie/generator/swagger/type.rb b/lib/apipie/generator/swagger/type.rb
new file mode 100644
index 000000000..a94bbc331
--- /dev/null
+++ b/lib/apipie/generator/swagger/type.rb
@@ -0,0 +1,16 @@
+class Apipie::Generator::Swagger::Type
+  attr_reader :str_format
+
+  def initialize(type, str_format = nil)
+    @type = type
+    @str_format = str_format
+  end
+
+  def to_s
+    @type
+  end
+
+  def ==(other)
+    other.to_s == self.to_s
+  end
+end
diff --git a/lib/apipie/generator/swagger/type_extractor.rb b/lib/apipie/generator/swagger/type_extractor.rb
new file mode 100644
index 000000000..7dc35bc17
--- /dev/null
+++ b/lib/apipie/generator/swagger/type_extractor.rb
@@ -0,0 +1,69 @@
+class Apipie::Generator::Swagger::TypeExtractor
+  TYPES = {
+    numeric: 'number',
+    hash: 'object',
+    array: 'array',
+    enum: 'enum',
+
+    # see https://github.com/OAI/OpenAPI-Specification/blob/master/versions/2.0.md#data-types
+    integer: Apipie::Generator::Swagger::Type.new('integer', 'int32'),
+    long: Apipie::Generator::Swagger::Type.new('integer', 'int64'),
+    number: Apipie::Generator::Swagger::Type.new('number'),
+    float: Apipie::Generator::Swagger::Type.new('number', 'float'),
+    double: Apipie::Generator::Swagger::Type.new('number', 'double'),
+    string: Apipie::Generator::Swagger::Type.new('string'),
+    byte: Apipie::Generator::Swagger::Type.new('string', 'byte'),
+    binary: Apipie::Generator::Swagger::Type.new('string', 'binary'),
+    boolean: Apipie::Generator::Swagger::Type.new('boolean'),
+    date: Apipie::Generator::Swagger::Type.new('string', 'date'),
+    dateTime: Apipie::Generator::Swagger::Type.new('string', 'date-time'),
+    password: Apipie::Generator::Swagger::Type.new('string', 'password')
+  }
+
+  # @param [<Apipie::Validator::BaseValidator>] validator
+  def initialize(validator)
+    @validator = validator
+  end
+
+  # @param [Hash<Symbol, Apipie::Generator::Swagger::Warning>] warnings
+  def extract_with_warnings(warnings = {})
+    if boolean? && warnings[:boolean].present?
+      Apipie::Generator::Swagger::WarningWriter.instance.warn(warnings[:boolean])
+    end
+
+    extract
+  end
+
+  private
+
+  def extract
+    expected_type = if string?
+                      :string
+                    elsif boolean?
+                      :boolean
+                    elsif enum?
+                      :enum
+                    else
+                      @validator.expected_type.to_sym
+                    end
+
+    TYPES[expected_type] || @validator.expected_type
+  end
+
+  def string?
+    @validator.blank?
+  end
+
+  def enum?
+    @validator.is_a?(Apipie::Validator::EnumValidator) ||
+      (@validator.respond_to?(:is_enum) && @validator.is_enum)
+  end
+
+  def boolean?
+    @_boolean ||= enum? && boolean_values?
+  end
+
+  def boolean_values?
+    @validator.values.to_set == Set.new([true, false])
+  end
+end
diff --git a/lib/apipie/swagger_generator.rb b/lib/apipie/swagger_generator.rb
index d1e9d1f53..893826b05 100644
--- a/lib/apipie/swagger_generator.rb
+++ b/lib/apipie/swagger_generator.rb
@@ -318,68 +318,21 @@ def swagger_op_id_for_path(http_method, path)
       http_method.downcase + path.gsub(/\//,'_').gsub(/:(\w+)/, '\1').gsub(/_$/,'')
     end
 
-    class SwaggerTypeWithFormat
-      attr_reader :str_format
-      def initialize(type, str_format)
-        @type = type
-        @str_format = str_format
-      end
-
-      def to_s
-        @type
-      end
-
-      def ==(other)
-        other.to_s == self.to_s
-      end
-    end
-
-    def lookup
-      @lookup ||= {
-        numeric: "number",
-        hash: "object",
-        array: "array",
-
-        # see https://github.com/OAI/OpenAPI-Specification/blob/master/versions/2.0.md#data-types
-        integer: SwaggerTypeWithFormat.new("integer", "int32"),
-        long: SwaggerTypeWithFormat.new("integer", "int64"),
-        number: SwaggerTypeWithFormat.new("number", nil),  # here just for completeness
-        float: SwaggerTypeWithFormat.new("number", "float"),
-        double: SwaggerTypeWithFormat.new("number", "double"),
-        string: SwaggerTypeWithFormat.new("string", nil),  # here just for completeness
-        byte: SwaggerTypeWithFormat.new("string", "byte"),
-        binary: SwaggerTypeWithFormat.new("string", "binary"),
-        boolean: SwaggerTypeWithFormat.new("boolean", nil),  # here just for completeness
-        date: SwaggerTypeWithFormat.new("string", "date"),
-        dateTime: SwaggerTypeWithFormat.new("string", "date-time"),
-        password: SwaggerTypeWithFormat.new("string", "password"),
-      }
-    end
-
-
     def swagger_param_type(param_desc)
-      if param_desc.nil?
-        raise("problem")
+      if param_desc.blank?
+        raise ArgumentError, 'param_desc is required'
       end
 
-      v = param_desc.validator
-      if v.nil?
-        return "string"
-      end
-
-      if v.class == Apipie::Validator::EnumValidator || (v.respond_to?(:is_enum?) && v.is_enum?)
-        if v.values - [true, false] == [] && [true, false] - v.values == []
-          warn_inferring_boolean(param_desc.name)
-          return "boolean"
-        else
-          return "enum"
-        end
-      elsif v.class == Apipie::Validator::HashValidator
-        # pp v
-      end
+      method_id = ruby_name_for_method(@current_method)
 
+      warning = Apipie::Generator::Swagger::Warning.for_code(
+        Apipie::Generator::Swagger::Warning::INFERRING_BOOLEAN_CODE,
+        method_id,
+        { parameter: param_desc.name }
+      )
 
-      return lookup[v.expected_type.to_sym] || v.expected_type
+      Apipie::Generator::Swagger::TypeExtractor.new(param_desc.validator).
+        extract_with_warnings({ boolean: warning })
     end
 
 
@@ -515,7 +468,7 @@ def save_field(entry, openapi_key, v, apipie_key=openapi_key, translate=false)
 
       swg_param_type = swagger_param_type(param_desc)
       swagger_def[:type] = swg_param_type.to_s
-      if (swg_param_type.is_a? SwaggerTypeWithFormat) && !swg_param_type.str_format.nil?
+      if (swg_param_type.is_a? Apipie::Generator::Swagger::Type) && !swg_param_type.str_format.nil?
         swagger_def[:format] = swg_param_type.str_format
       end
 
diff --git a/spec/lib/generator/swagger/type_extractor_spec.rb b/spec/lib/generator/swagger/type_extractor_spec.rb
new file mode 100644
index 000000000..ab7fdc6f4
--- /dev/null
+++ b/spec/lib/generator/swagger/type_extractor_spec.rb
@@ -0,0 +1,61 @@
+require 'spec_helper'
+
+describe Apipie::Generator::Swagger::TypeExtractor do
+  let(:validator) {}
+  let(:extractor) { described_class.new(validator) }
+
+  describe '#extarct_with_warnings' do
+    let(:warnings) { {} }
+
+    before { Apipie.configuration.swagger_suppress_warnings = false }
+
+    subject { extractor.extract_with_warnings(warnings) }
+
+    it { is_expected.to eq(Apipie::Generator::Swagger::TypeExtractor::TYPES[:string]) }
+
+    context "when enum validator is used" do
+      let(:enum_values) { ["Name"] }
+
+      context "of type Apipie::Validator::EnumValidator" do
+        let(:validator) { Apipie::Validator::EnumValidator.new(nil, enum_values) }
+
+        it { is_expected.to eq("enum") }
+      end
+
+      context "that responds to is_enum?" do
+        let(:validator) do
+          Apipie::ResponseDescriptionAdapter::PropDesc::Validator.new('some-type', enum_values)
+        end
+
+        it 'returns an enum type' do
+          expect(subject).to eq(Apipie::Generator::Swagger::TypeExtractor::TYPES[:enum])
+        end
+
+        context 'and has `true`, `false` as values' do
+          let(:param_description_name) { :visible }
+          let(:enum_values) { [true, false] }
+
+          it 'returns a boolean type' do
+            expect(subject).to eq(Apipie::Generator::Swagger::TypeExtractor::TYPES[:boolean])
+          end
+
+          context 'and a boolean warning is passed' do
+            let(:boolean_warning) do
+              Apipie::Generator::Swagger::Warning.for_code(
+                Apipie::Generator::Swagger::Warning::INFERRING_BOOLEAN_CODE,
+                'SampleController#action',
+                { parameter: 'some-param' }
+              )
+            end
+
+            let(:warnings) { { boolean: boolean_warning } }
+
+            it 'outputs the warning' do
+              expect { subject }.to output(boolean_warning.warning_message).to_stderr
+            end
+          end
+        end
+      end
+    end
+  end
+end