diff --git a/README.rdoc b/README.rdoc
index efb9ab1..b6933f0 100644
--- a/README.rdoc
+++ b/README.rdoc
@@ -71,6 +71,9 @@ driver tests will then use some of the data files from that project when it
 runs BSON tests. You can delete this directory at any time if you don't want
 to run those tests any more.
 
+Additionally, the script bin/validate is used by the mongo-qa project's
+validator script.
+
 
 = Documentation
 
diff --git a/bin/validate b/bin/validate
index 3944048..2d25548 100755
--- a/bin/validate
+++ b/bin/validate
@@ -6,6 +6,10 @@
 # converts it into a Ruby OrderedHash, runs that through the BSON
 # serialization code, and writes the BSON bytes to somefile.bson.
 #
+# In addition, this script takes the generated BSON, reads it in then writes
+# it back out to a temp BSON file. If they are different, we report that error
+# to STDOUT.
+#
 # This script is used by the mongo-qa project
 # (http://github.com/mongodb/mongo-qa).
 
@@ -13,6 +17,35 @@ $LOAD_PATH[0,0] = File.join(File.dirname(__FILE__), '..', 'lib')
 require 'mongo'
 require 'mongo/util/xml_to_ruby'
 
-obj = File.open(ARGV[0], 'r') { |f| XMLToRuby.new.xml_to_ruby(f) }
+if ARGV.length < 2
+  $stderr.puts "usage: validate somefile.xson somefile.bson"
+  exit 1
+end
+
+# Translate the .xson XML into a Ruby object, turn that object into BSON, and
+# write the BSON to the file as requested.
+obj = File.open(ARGV[0], 'rb') { |f| XMLToRuby.new.xml_to_ruby(f) }
 bson = BSON.new.serialize(obj).to_a
 File.open(ARGV[1], 'wb') { |f| bson.each { |b| f.putc(b) } }
+
+# Now the additional testing. Read the generated BSON back in, deserialize it,
+# and re-serialize the results. Compare that BSON with the BSON from the file
+# we output.
+bson = File.open(ARGV[1], 'rb') { |f| f.read }
+bson = if RUBY_VERSION >= '1.9'
+         bson.bytes.to_a
+       else
+         bson.split(//).collect { |c| c[0] }
+       end
+
+# Turn the Ruby object into BSON bytes and compare with the BSON bytes from
+# the file.
+bson_from_ruby = BSON.new.serialize(obj).to_a
+
+if bson.length != bson_from_ruby.length
+  $stderr.puts "error: round-trip BSON lengths differ when testing #{ARGV[0]}"
+  exit 1
+elsif bson != bson_from_ruby
+  $stderr.puts "error: round-trip BSON contents differ when testing #{ARGV[0]}"
+  exit 1
+end