diff --git a/lib/bson/types/object_id.rb b/lib/bson/types/object_id.rb
index 5de7f66241..6e44efa515 100644
--- a/lib/bson/types/object_id.rb
+++ b/lib/bson/types/object_id.rb
@@ -51,7 +51,7 @@ def initialize(data=nil, time=nil)
     #
     # @return [Boolean]
     def self.legal?(str)
-      str =~ /^[0-9a-f]{24}$/i ? true : false
+      str =~ /\A[0-9a-f]{24}\z/i ? true : false
     end
 
     # Create an object id from the given time. This is useful for doing range
diff --git a/test/bson/object_id_test.rb b/test/bson/object_id_test.rb
index 5626c61b84..06de831cc9 100644
--- a/test/bson/object_id_test.rb
+++ b/test/bson/object_id_test.rb
@@ -93,6 +93,9 @@ def test_illegal_from_string
     assert_raise InvalidObjectId do
       ObjectId.from_string("")
     end
+    assert_raise InvalidObjectId do
+      ObjectId.from_string("a"*24+"\na")
+    end
   end
 
   def test_from_string_with_object_id