Index: lang/rust/Makefile
===================================================================
--- lang/rust/Makefile
+++ lang/rust/Makefile
@@ -142,6 +142,16 @@
 		${WRKSRC}/src/bootstrap/install.rs
 
 do-configure:
+# Sanity check that the running kernel was built with the necessary
+# syscall compat option.
+.if ${OPSYS} == FreeBSD && ${OSVERSION} >= 1200000
+	@${PRINTF} '#include <sys/syscall.h>\n#include <errno.h>\n#include <unistd.h>\n\
+	int main(void) { return syscall(SYS_freebsd11_mknod, "", 0, 0) < 0 && errno == ENOSYS; }' | \
+	${CC} -o ${WRKSRC}/compat11_canary -xc - && ${WRKSRC}/compat11_canary || (\
+		${ECHO_MSG} "=> Sanity check failed: kernel is missing COMPAT_FREEBSD11"; \
+		${ECHO_MSG} "=> Aborting build"; \
+		${FALSE})
+.endif
 	@${ECHO_CMD} '[build]' > ${WRKSRC}/config.toml
 	@${ECHO_CMD} 'vendor=true' >> ${WRKSRC}/config.toml
 	@${ECHO_CMD} 'extended=true' >> ${WRKSRC}/config.toml