diff --git a/lib/uri/mailto.rb b/lib/uri/mailto.rb
index cb8024f..a20e0ef 100644
--- a/lib/uri/mailto.rb
+++ b/lib/uri/mailto.rb
@@ -222,7 +222,8 @@ def set_headers(v)
       @headers = []
       if v
         v.split('&').each do |x|
-          @headers << x.split(/=/, 2)
+          name, value = x.split(/=/, 2)
+          @headers << [name, value || '']
         end
       end
     end
@@ -266,18 +267,20 @@ def to_s
     #   # => "To: ruby-list@ruby-lang.org\nSubject: subscribe\nCc: myaddr\n\n\n"
     #
     def to_mailtext
-      to = URI.decode_www_form_component(@to)
+      to = URI.decode_www_form_component(@to.to_s)
       head = ''
       body = ''
       @headers.each do |x|
-        case x[0]
+        name = x[0].to_s
+        value = x[1].to_s
+        case name
         when 'body'
-          body = URI.decode_www_form_component(x[1])
+          body = URI.decode_www_form_component(value)
         when 'to'
-          to << ', ' + URI.decode_www_form_component(x[1])
+          to << ', ' + URI.decode_www_form_component(value)
         else
-          head << URI.decode_www_form_component(x[0]).capitalize + ': ' +
-            URI.decode_www_form_component(x[1])  + "\n"
+          head << URI.decode_www_form_component(name).capitalize + ': ' +
+            URI.decode_www_form_component(value)  + "\n"
         end
       end
 
diff --git a/test/uri/test_mailto.rb b/test/uri/test_mailto.rb
index 6cd3352..fd5c7e6 100644
--- a/test/uri/test_mailto.rb
+++ b/test/uri/test_mailto.rb
@@ -253,6 +253,16 @@ def test_to_mailtext
       u.to_mailtext
   end
 
+  def test_to_mailtext_with_header_name_only
+    u = URI.parse('mailto:ruby-list@ruby-lang.org?Subject')
+    assert_equal [['Subject', '']], u.headers
+    assert_equal "To: ruby-list@ruby-lang.org\nSubject: \n\n\n", u.to_mailtext
+
+    u = URI.parse('mailto:ruby-list@ruby-lang.org?body&cc=myaddr')
+    assert_equal [['body', ''], ['cc', 'myaddr']], u.headers
+    assert_equal "To: ruby-list@ruby-lang.org\nCc: myaddr\n\n\n", u.to_mailtext
+  end
+
   def test_select
     u = URI.parse('mailto:joe@example.com?cc=bob@example.com&body=hello')
     assert_equal(uri_to_ary(u), u.select(*u.component))