Are you on OS X? Apple stopped shipping an OpenSSL header that's needed by a Servo dependency (https://github.com/servo/servo/issues/7303 https://github.com/ser

Are you on OS X? Apple stopped shipping an OpenSSL header that's needed by a Servo dependency (https://github.com/servo/servo/issues/7303 https://github.com/servo/servo/issues/7303). If you're using Homebrew, you should be able to build by manually pointing to a brew-installed copy of OpenSSL: export OPENSSL_INCLUDE_DIR=$(brew --prefix openssl)/include export DEP_OPENSSL_INCLUDE=$(brew --prefix openssl)/include ./mach build Alternatively, if you don't mind shadowing the system's default version of OpenSSL, you can try `brew link --force openssl`.