Make a custom Eclipse builder conditional on the success of another builder

I've added a custom builder to my Flex Builder 3 (Eclipse 3.4) project that uploads the built files to a test server for remote debugging, and my custom builder appears after the "Flex" builder in my project properties, and works great after a successful Flex build. However my custom builder runs all the time, even when there was an error in the Flex build. Is there some way I can make the custom builder only run if the main builde开发者_开发技巧r built successfully?