diff --git a/lib/ougai/formatters/base.rb b/lib/ougai/formatters/base.rb
index 36d6758..633f483 100644
--- a/lib/ougai/formatters/base.rb
+++ b/lib/ougai/formatters/base.rb
@@ -6,10 +6,11 @@ module Ougai
   module Formatters
     class Base < Logger::Formatter
       attr_accessor :trace_indent, :trace_max_lines
+      attr_reader :app_name, :hostname
 
       def initialize(app_name = nil, hostname = nil)
         @app_name = app_name || File.basename($0, ".rb")
-        @hostname = hostname || Socket.gethostname
+        @hostname = hostname || Socket.gethostname.force_encoding('UTF-8')
         @trace_indent = 2
         @trace_max_lines = 100
       end
diff --git a/lib/ougai/version.rb b/lib/ougai/version.rb
index fd29a83..b270d54 100644
--- a/lib/ougai/version.rb
+++ b/lib/ougai/version.rb
@@ -1,3 +1,3 @@
 module Ougai
-  VERSION = "0.7.3"
+  VERSION = "0.7.4"
 end
diff --git a/spec/formatters/base_spec.rb b/spec/formatters/base_spec.rb
new file mode 100644
index 0000000..3241f77
--- /dev/null
+++ b/spec/formatters/base_spec.rb
@@ -0,0 +1,49 @@
+require 'spec_helper'
+
+describe Ougai::Formatters::Base do
+  subject { described_class.new(app_name, hostname) }
+
+  context 'without arguments and hostname contains a UTF-8 char' do
+    let (:app_name) { nil }
+    let (:hostname) { nil }
+
+    it 'has default app_name and default hostname' do
+      myhostname = "Taro\xE2\x80\x99s-MacBook".force_encoding('ASCII-8BIT')
+      allow(Socket).to receive(:gethostname).and_return(myhostname)
+      expect(subject.app_name).to eq('rspec')
+      expect(subject.hostname).to eq("Taro’s-MacBook")
+    end
+  end
+
+  context 'with app_name' do
+    let (:app_name) { 'myapp' }
+    let (:hostname) { nil }
+
+    it 'has specified app_name and default hostname' do
+      myhostname = "Hanako's PC".encode('ASCII-8BIT')
+      allow(Socket).to receive(:gethostname).and_return(myhostname)
+      expect(subject.app_name).to eq('myapp')
+      expect(subject.hostname).to eq("Hanako's PC")
+    end
+  end
+
+  context 'with hostname' do
+    let (:app_name) { nil }
+    let (:hostname) { 'myhost' }
+
+    it 'has default app_name and specified hostname' do
+      expect(subject.app_name).to eq('rspec')
+      expect(subject.hostname).to eq('myhost')
+    end
+  end
+
+  context 'with app_name and hostname' do
+    let (:app_name) { 'myapp' }
+    let (:hostname) { 'myhost' }
+
+    it 'has specified app_name and specified hostname' do
+      expect(subject.app_name).to eq('myapp')
+      expect(subject.hostname).to eq('myhost')
+    end
+  end
+end