diff --git a/lang/funcs/core/sys/uptime_fact_darwin.go b/lang/funcs/core/sys/uptime_fact_darwin.go
new file mode 100644
index 00000000..9b58656a
--- /dev/null
+++ b/lang/funcs/core/sys/uptime_fact_darwin.go
@@ -0,0 +1,47 @@
+// Mgmt
+// Copyright (C) 2013-2019+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+// +build darwin
+
+package coresys
+
+import (
+	"fmt"
+	"syscall"
+	"time"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+func uptime() (int64, error) {
+	// get time of boot struct
+	rawBoottime, err := unix.SysctlRaw("kern.boottime")
+	if err != nil {
+		return 0, err
+	}
+
+	// make sure size is correct
+	var boottime syscall.Timeval
+	if len(rawBoottime) != int(unsafe.Sizeof(boottime)) {
+		return 0, fmt.Errorf("invalid boottime encountered while calculating uptime")
+	}
+
+	// uptime is difference between current time and boot time
+	boottime = *(*syscall.Timeval)(unsafe.Pointer(&rawBoottime[0]))
+	return time.Now().Unix() - boottime.Sec, nil
+}