Index: head/Mk/Scripts/rust-compat11-canary.sh
===================================================================
--- head/Mk/Scripts/rust-compat11-canary.sh
+++ head/Mk/Scripts/rust-compat11-canary.sh
@@ -0,0 +1,27 @@
+#!/bin/sh
+# MAINTAINER: rust@FreeBSD.org
+# $FreeBSD$
+set -eu
+
+if [ "${OPSYS}" != FreeBSD ] || [ "${OSVERSION}" -lt 1200000 ]; then
+	exit 0
+fi
+
+cat <<EOF | ${CC} -o "${WRKDIR}/compat11_canary" -xc -
+#include <sys/syscall.h>
+#include <errno.h>
+#include <unistd.h>
+
+int
+main(void)
+{
+	return syscall(SYS_freebsd11_mknod, "", 0, 0) < 0 && errno == ENOSYS;
+}
+EOF
+# Canary might be aborted with SIGSYS
+ulimit -c 0
+if ! "${WRKDIR}/compat11_canary"; then
+	echo "=> Sanity check failed: kernel is missing COMPAT_FREEBSD11"
+	echo "=> Aborting build"
+	exit 1
+fi
Index: head/Mk/Uses/cargo.mk
===================================================================
--- head/Mk/Uses/cargo.mk
+++ head/Mk/Uses/cargo.mk
@@ -247,6 +247,9 @@
 # configure hook.  Place a config file for overriding crates-io index
 # by local source directory.
 cargo-configure:
+# Check that the running kernel has COMPAT_FREEBSD11 required by lang/rust post-ino64
+	@${SETENV} CC="${CC}" OPSYS="${OPSYS}" OSVERSION="${OSVERSION}" WRKDIR="${WRKDIR}" \
+		${SH} ${SCRIPTSDIR}/rust-compat11-canary.sh
 	@${MKDIR} ${WRKDIR}/.cargo
 	@${ECHO_CMD} "[source.cargo]" > ${WRKDIR}/.cargo/config
 	@${ECHO_CMD} "directory = '${CARGO_VENDOR_DIR}'" >> ${WRKDIR}/.cargo/config
Index: head/Mk/bsd.gecko.mk
===================================================================
--- head/Mk/bsd.gecko.mk
+++ head/Mk/bsd.gecko.mk
@@ -376,6 +376,11 @@
 	@${REINPLACE_CMD} 's,"files":{[^}]*},"files":{},' \
 		${MOZSRC}/third_party/rust/*/.cargo-checksum.json
 
+pre-configure-script:
+# Check that the running kernel has COMPAT_FREEBSD11 required by lang/rust post-ino64
+	@${SETENV} CC="${CC}" OPSYS="${OPSYS}" OSVERSION="${OSVERSION}" WRKDIR="${WRKDIR}" \
+		${SH} ${SCRIPTSDIR}/rust-compat11-canary.sh
+
 post-install-script: gecko-create-plist
 
 gecko-create-plist:
Index: head/lang/rust/Makefile
===================================================================
--- head/lang/rust/Makefile
+++ head/lang/rust/Makefile
@@ -142,6 +142,9 @@
 		${WRKSRC}/src/bootstrap/install.rs
 
 do-configure:
+# Check that the running kernel has COMPAT_FREEBSD11 required by lang/rust post-ino64
+	@${SETENV} CC="${CC}" OPSYS="${OPSYS}" OSVERSION="${OSVERSION}" WRKDIR="${WRKDIR}" \
+		${SH} ${SCRIPTSDIR}/rust-compat11-canary.sh
 	@${ECHO_CMD} '[build]' > ${WRKSRC}/config.toml
 	@${ECHO_CMD} 'vendor=true' >> ${WRKSRC}/config.toml
 	@${ECHO_CMD} 'extended=true' >> ${WRKSRC}/config.toml