diff --git a/lib/mongo/cursor.rb b/lib/mongo/cursor.rb
index bcff827..bbbd39b 100644
--- a/lib/mongo/cursor.rb
+++ b/lib/mongo/cursor.rb
@@ -350,10 +350,15 @@ module Mongo
     #
     # @param opt a valid query option
     #
+    # @raise InvalidOperation if this method is run after the cursor has bee
+    #   iterated for the first time.
+    #
     # @return [Integer] the current value of the options bitfield for this cursor.
     #
     # @see http://www.mongodb.org/display/DOCS/Mongo+Wire+Protocol#MongoWireProtocol-Mongo::Constants::OPQUERY
     def add_option(opt)
+      check_modifiable
+
       @options |= opt
       @options
     end
@@ -362,10 +367,15 @@ module Mongo
     #
     # @param opt a valid query option
     #
+    # @raise InvalidOperation if this method is run after the cursor has bee
+    #   iterated for the first time.
+    #
     # @return [Integer] the current value of the options bitfield for this cursor.
     #
     # @see http://www.mongodb.org/display/DOCS/Mongo+Wire+Protocol#MongoWireProtocol-Mongo::Constants::OPQUERY
     def remove_option(opt)
+      check_modifiable
+
       @options &= ~opt
       @options
     end
diff --git a/test/cursor_test.rb b/test/cursor_test.rb
index 9bf14fb..c78d4ce 100644
--- a/test/cursor_test.rb
+++ b/test/cursor_test.rb
@@ -39,6 +39,15 @@ class CursorTest < Test::Unit::TestCase
     assert_equal OP_QUERY_EXHAUST, c.options & OP_QUERY_EXHAUST
     c.remove_option(OP_QUERY_EXHAUST)
     assert_equal 0, c.options & OP_QUERY_EXHAUST
+
+    c.next
+    assert_raise Mongo::InvalidOperation do
+      c.add_option(OP_QUERY_EXHAUST)
+    end
+
+    assert_raise Mongo::InvalidOperation do
+      c.add_option(OP_QUERY_EXHAUST)
+    end
   end
 
   def test_inspect