Compiler warnings are an effective tool for developers to catch potential security, compatibility, and correctness problems — however a challenging problem is ensuring that specific warnings are actually enabled across codebases and that diagnostics are addressed over time. This talk describes how we have extended Clang's diagnostic infrastructure to enable developers to build a policy enforcement system that supports issue baselining (i.e., reporting only newly introduced warnings) and backslide prevention (informing project maintainers when a warning has accidentally been turned off).