diff --git a/lib/securerandom.rb b/lib/securerandom.rb
index 99e54db..5e96ef8 100644
--- a/lib/securerandom.rb
+++ b/lib/securerandom.rb
@@ -137,7 +137,7 @@ module SecureRandom
   # If secure random number generator is not available,
   # NotImplementedError is raised.
   def self.hex(n=nil)
-    random_bytes(n).unpack("H*")[0]
+    random_bytes(n).unpack("H*")[0].force_encoding(Encoding::US_ASCII)
   end
 
   # SecureRandom.base64 generates a random base64 string.
diff --git a/test/test_securerandom.rb b/test/test_securerandom.rb
index f3e1bf0..f3c9a1a 100644
--- a/test/test_securerandom.rb
+++ b/test/test_securerandom.rb
@@ -111,6 +111,10 @@ end
     end
   end
 
+  def test_hex_encoding
+    assert_equal(Encoding::US_ASCII, @it.hex.encoding)
+  end
+
   def test_s_base64
     assert_equal(16, @it.base64.unpack('m*')[0].size)
     17.times do |idx|