diff --git a/lib/optparse.rb b/lib/optparse.rb
index 238fa1e..4da233e 100644
--- a/lib/optparse.rb
+++ b/lib/optparse.rb
@@ -1148,6 +1148,7 @@ def initialize(banner = nil, width = 32, indent = ' ' * 4)
     @summary_indent = indent
     @default_argv = ARGV
     @require_exact = false
+    @raise_unknown = true
     add_officious
     yield self if block_given?
   end
@@ -1225,6 +1226,9 @@ def self.reject(*args, &blk) top.reject(*args, &blk) end
   # abbreviated long option as short option).
   attr_accessor :require_exact
 
+  # Whether to raise at unknown option.
+  attr_accessor :raise_unknown
+
   #
   # Heading banner preceding summary.
   #
@@ -1639,9 +1643,11 @@ def parse_in_order(argv = default_argv, setter = nil, &nonopt)  # :nodoc:
           begin
             sw, = complete(:long, opt, true)
             if require_exact && !sw.long.include?(arg)
+              throw :terminate, arg unless raise_unknown
               raise InvalidOption, arg
             end
           rescue ParseError
+            throw :terminate, arg unless raise_unknown
             raise $!.set_option(arg, true)
           end
           begin
@@ -1673,6 +1679,7 @@ def parse_in_order(argv = default_argv, setter = nil, &nonopt)  # :nodoc:
               end
             end
           rescue ParseError
+            throw :terminate, arg unless raise_unknown
             raise $!.set_option(arg, true)
           end
           begin
diff --git a/test/optparse/test_optparse.rb b/test/optparse/test_optparse.rb
index 5f5ea18..285c4a5 100644
--- a/test/optparse/test_optparse.rb
+++ b/test/optparse/test_optparse.rb
@@ -98,6 +98,18 @@ def test_require_exact
     assert_raise(OptionParser::InvalidOption) {@opt.parse(%w(-z foo))}
   end
 
+  def test_raise_unknown
+    @opt.def_option('--foo [ARG]') {|arg| @foo = arg}
+    assert @opt.raise_unknown
+
+    @opt.raise_unknown = false
+    assert_equal(%w[--bar], @opt.parse(%w[--foo --bar]))
+    assert_nil(@foo)
+
+    assert_equal(%w[--bar], @opt.parse(%w[--foo x --bar]))
+    assert_equal("x", @foo)
+  end
+
   def test_nonopt_pattern
     @opt.def_option(/^[^-]/) do |arg|
       assert(false, "Never gets called")