diff --git a/Gemfile.lock b/Gemfile.lock
index b729a7e..8af6f90 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -6,15 +6,20 @@ PATH
 GEM
   remote: http://rubygems.org/
   specs:
-    diff-lcs (1.1.2)
-    rspec (2.5.0)
-      rspec-core (~> 2.5.0)
-      rspec-expectations (~> 2.5.0)
-      rspec-mocks (~> 2.5.0)
-    rspec-core (2.5.1)
-    rspec-expectations (2.5.0)
-      diff-lcs (~> 1.1.2)
-    rspec-mocks (2.5.0)
+    diff-lcs (1.3)
+    rspec (3.6.0)
+      rspec-core (~> 3.6.0)
+      rspec-expectations (~> 3.6.0)
+      rspec-mocks (~> 3.6.0)
+    rspec-core (3.6.0)
+      rspec-support (~> 3.6.0)
+    rspec-expectations (3.6.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.6.0)
+    rspec-mocks (3.6.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.6.0)
+    rspec-support (3.6.0)
 
 PLATFORMS
   ruby
diff --git a/lib/ruby-rtf/parser.rb b/lib/ruby-rtf/parser.rb
index 54a375c..f0e51e7 100644
--- a/lib/ruby-rtf/parser.rb
+++ b/lib/ruby-rtf/parser.rb
@@ -10,12 +10,14 @@ class Parser
 
     attr_reader :doc
 
-    def initialize
+    # @param unknown_control_warning_enabled [Boolean] Whether to write unknown control directive warnings to STDERR
+    def initialize(unknown_control_warning_enabled: true)
       # default_mods needs to be the same has in the formatting stack and in
       # the current_section modifiers or the first stack ends up getting lost.
       default_mods = {}
       @formatting_stack = [default_mods]
       @current_section = {:text => '', :modifiers => default_mods}
+      @unknown_control_warning_enabled = unknown_control_warning_enabled
 
       @seen = {}
 
@@ -292,7 +294,9 @@ def handle_control(name, val, src, current_pos)
       else
         unless @seen[name]
           @seen[name] = true
-          STDERR.puts "Unknown control #{name.inspect} with #{val} at #{current_pos}"
+          if @unknown_control_warning_enabled
+            warn "Unknown control #{name.inspect} with #{val} at #{current_pos}"
+          end
         end
       end
       current_pos
diff --git a/spec/parser_spec.rb b/spec/parser_spec.rb
index 741b178..900174f 100644
--- a/spec/parser_spec.rb
+++ b/spec/parser_spec.rb
@@ -6,6 +6,26 @@
   let(:parser) { RubyRTF::Parser.new }
   let(:doc) { parser.doc }
 
+  context 'with input containing invalid control directives' do
+    let(:parser) { RubyRTF::Parser.new(unknown_control_warning_enabled: unknown_control_warning_enabled) }
+    let(:doc) { '{\rtf1\ansi\xxxxx0}' }
+
+    context 'with unknown_control_warning_enabled = false' do
+      let(:unknown_control_warning_enabled) { false }
+
+      it 'does not write anything to stderr' do
+        expect { parser.parse(doc) }.not_to output.to_stderr
+      end
+    end
+    context 'with unknown_control_warning_enabled = true' do
+      let(:unknown_control_warning_enabled) { true }
+
+      it 'writes message to stderr' do
+        expect { parser.parse(doc) }.to output("Unknown control :xxxxx with 0 at 18\n").to_stderr
+      end
+    end
+  end
+
   it 'parses hello world' do
     src = '{\rtf1\ansi\deff0 {\fonttbl {\f0 Times New Roman;}}\f0 \fs60 Hello, World!}'
     lambda { parser.parse(src) }.should_not raise_error
@@ -14,7 +34,7 @@
   it 'returns a RTF::Document' do
     src = '{\rtf1\ansi\deff0 {\fonttbl {\f0 Times New Roman;}}\f0 \fs60 Hello, World!}'
     d = parser.parse(src)
-    d.is_a?(RubyRTF::Document).should be_true
+    d.is_a?(RubyRTF::Document).should  == true
   end
 
   it 'parses a default font (\deffN)' do
@@ -76,21 +96,21 @@
 
       section = parser.parse(src).sections
       section[0][:modifiers][:font_size].should == 30
-      section[0][:modifiers][:bold].should be_true
-      section[0][:modifiers].has_key?(:italic).should be_false
-      section[0][:modifiers].has_key?(:underline).should be_false
+      section[0][:modifiers][:bold].should == true
+      section[0][:modifiers].has_key?(:italic).should == false
+      section[0][:modifiers].has_key?(:underline).should == false
       section[0][:text].should == 'Hello '
 
       section[1][:modifiers][:font_size].should == 15
-      section[1][:modifiers][:italic].should be_true
-      section[1][:modifiers][:bold].should be_true
-      section[1][:modifiers].has_key?(:underline).should be_false
+      section[1][:modifiers][:italic].should == true
+      section[1][:modifiers][:bold].should == true
+      section[1][:modifiers].has_key?(:underline).should == false
       section[1][:text].should == 'World'
 
       section[2][:modifiers][:font_size].should == 30
-      section[2][:modifiers][:bold].should be_true
-      section[2][:modifiers][:underline].should be_true
-      section[2][:modifiers].has_key?(:italic).should be_false
+      section[2][:modifiers][:bold].should == true
+      section[2][:modifiers][:underline].should == true
+      section[2][:modifiers].has_key?(:italic).should == false
       section[2][:text].should == 'Goodbye, cruel world.'
     end
 
@@ -106,16 +126,16 @@
 
       it 'should parse jpeg' do
         section = parser.parse(src_jpeg).sections
-        section[0][:modifiers][:picture].should be_true
+        section[0][:modifiers][:picture].should == true
         section[0][:modifiers][:picture_format].should == 'jpeg'
       end
 
       it 'should parse bmp' do
         section = parser.parse(src_bitmap).sections
-        section[0][:modifiers][:picture].should be_true
+        section[0][:modifiers][:picture].should == true
         section[0][:modifiers][:picture_format].should == 'bmp'
         section = parser.parse(src_bitmap).sections
-        section[0][:modifiers][:picture].should be_true
+        section[0][:modifiers][:picture].should == true
         section[0][:modifiers][:picture_format].should == 'bmp'
       end
 
@@ -144,12 +164,12 @@
     it 'clears ul with ul0' do
       src = '{\rtf1 \ul\b Hello\b0\ul0 World}'
       section = parser.parse(src).sections
-      section[0][:modifiers][:bold].should be_true
-      section[0][:modifiers][:underline].should be_true
+      section[0][:modifiers][:bold].should == true
+      section[0][:modifiers][:underline].should == true
       section[0][:text].should == 'Hello'
 
-      section[1][:modifiers].has_key?(:bold).should be_false
-      section[1][:modifiers].has_key?(:underline).should be_false
+      section[1][:modifiers].has_key?(:bold).should == false
+      section[1][:modifiers].has_key?(:underline).should == false
       section[1][:text].should == 'World'
     end
   end
@@ -376,7 +396,7 @@
       doc = parser.parse(src)
 
       clr = doc.colour_table[0]
-      clr.use_default?.should be_true
+      clr.use_default?.should == true
 
       clr = doc.colour_table[1]
       clr.red.should == 255
@@ -456,17 +476,17 @@
 
     it 'sets bold' do
       parser.handle_control(:b, nil, nil, 0)
-      parser.current_section[:modifiers][:bold].should be_true
+      parser.current_section[:modifiers][:bold].should == true
     end
 
     it 'sets underline' do
       parser.handle_control(:ul, nil, nil, 0)
-      parser.current_section[:modifiers][:underline].should be_true
+      parser.current_section[:modifiers][:underline].should == true
     end
 
     it 'sets italic' do
       parser.handle_control(:i, nil, nil, 0)
-      parser.current_section[:modifiers][:italic].should be_true
+      parser.current_section[:modifiers][:italic].should == true
     end
 
     %w(rquote lquote).each do |quote|
@@ -474,7 +494,7 @@
         parser.current_section[:text] = 'My code'
         parser.handle_control(quote.to_sym, nil, nil, 0)
         doc.sections.last[:text].should == "'"
-        doc.sections.last[:modifiers][quote.to_sym].should be_true
+        doc.sections.last[:modifiers][quote.to_sym].should == true
       end
     end
 
@@ -483,7 +503,7 @@
         parser.current_section[:text] = 'My code'
         parser.handle_control(quote.to_sym, nil, nil, 0)
         doc.sections.last[:text].should == '"'
-        doc.sections.last[:modifiers][quote.to_sym].should be_true
+        doc.sections.last[:modifiers][quote.to_sym].should == true
       end
     end
 
@@ -530,7 +550,7 @@
         parser.current_section[:text] = "end."
         parser.handle_control(:uc, 0, nil, 0)
         parser.handle_control(:u, 8232, nil, 0)
-        doc.sections.last[:modifiers][:newline].should be_true
+        doc.sections.last[:modifiers][:newline].should == true
         doc.sections.last[:text].should == "\n"
       end
     end
@@ -540,7 +560,7 @@
         it "sets from #{type}" do
           parser.current_section[:text] = "end."
           parser.handle_control(type.to_sym, nil, nil, 0)
-          doc.sections.last[:modifiers][:newline].should be_true
+          doc.sections.last[:modifiers][:newline].should == true
           doc.sections.last[:text].should == "\n"
         end
       end
@@ -555,7 +575,7 @@
     it 'inserts a \tab' do
       parser.current_section[:text] = "end."
       parser.handle_control(:tab, nil, nil, 0)
-      doc.sections.last[:modifiers][:tab].should be_true
+      doc.sections.last[:modifiers][:tab].should == true
       doc.sections.last[:text].should == "\t"
     end
 
@@ -563,7 +583,7 @@
       parser.current_section[:text] = "end."
       parser.handle_control(:super, nil, nil, 0)
 
-      parser.current_section[:modifiers][:superscript].should be_true
+      parser.current_section[:modifiers][:superscript].should == true
       parser.current_section[:text].should == ""
     end
 
@@ -571,7 +591,7 @@
       parser.current_section[:text] = "end."
       parser.handle_control(:sub, nil, nil, 0)
 
-      parser.current_section[:modifiers][:subscript].should be_true
+      parser.current_section[:modifiers][:subscript].should == true
       parser.current_section[:text].should == ""
     end
 
@@ -579,7 +599,7 @@
       parser.current_section[:text] = "end."
       parser.handle_control(:strike, nil, nil, 0)
 
-      parser.current_section[:modifiers][:strikethrough].should be_true
+      parser.current_section[:modifiers][:strikethrough].should == true
       parser.current_section[:text].should == ""
     end
 
@@ -587,21 +607,21 @@
       parser.current_section[:text] = "end."
       parser.handle_control(:scaps, nil, nil, 0)
 
-      parser.current_section[:modifiers][:smallcaps].should be_true
+      parser.current_section[:modifiers][:smallcaps].should == true
       parser.current_section[:text].should == ""
     end
 
     it 'inserts an \emdash' do
       parser.current_section[:text] = "end."
       parser.handle_control(:emdash, nil, nil, 0)
-      doc.sections.last[:modifiers][:emdash].should be_true
+      doc.sections.last[:modifiers][:emdash].should == true
       doc.sections.last[:text].should == "--"
     end
 
     it 'inserts an \endash' do
       parser.current_section[:text] = "end."
       parser.handle_control(:endash, nil, nil, 0)
-      doc.sections.last[:modifiers][:endash].should be_true
+      doc.sections.last[:modifiers][:endash].should == true
       doc.sections.last[:text].should == "-"
     end
 
@@ -627,8 +647,8 @@
         parser.current_section[:modifiers][:italic] = true
         parser.handle_control(type.to_sym, nil, nil, 0)
 
-        parser.current_section[:modifiers].has_key?(:bold).should be_false
-        parser.current_section[:modifiers].has_key?(:italic).should be_false
+        parser.current_section[:modifiers].has_key?(:bold).should == false
+        parser.current_section[:modifiers].has_key?(:italic).should == false
       end
     end
 
@@ -723,7 +743,7 @@
       it 'handles :~' do
         parser.current_section[:text] = "end."
         parser.handle_control(:~, nil, nil, 0)
-        doc.sections.last[:modifiers][:nbsp].should be_true
+        doc.sections.last[:modifiers][:nbsp].should == true
         doc.sections.last[:text].should == " "
       end
     end