diff --git a/src/internal/syscall/unix/fcntl_linux_32bit.go b/src/internal/syscall/unix/fcntl_linux_32bit.go
new file mode 100644
index 0000000000..6c75afc2ab
--- /dev/null
+++ b/src/internal/syscall/unix/fcntl_linux_32bit.go
@@ -0,0 +1,16 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// On 32-bit Linux systems, use SYS_FCNTL64.
+// If you change the build tags here, see syscall/flock_linux_32bit.go.
+
+// +build linux,386 linux,arm linux,mips linux,mipsle
+
+package unix
+
+import "syscall"
+
+func init() {
+	FcntlSyscall = syscall.SYS_FCNTL64
+}
diff --git a/src/internal/syscall/unix/nonblocking.go b/src/internal/syscall/unix/nonblocking.go
index bcc350b56e..545445204f 100644
--- a/src/internal/syscall/unix/nonblocking.go
+++ b/src/internal/syscall/unix/nonblocking.go
@@ -8,8 +8,12 @@ package unix
 
 import "syscall"
 
+// FcntlSyscall is the number for the fcntl system call. This is
+// usually SYS_FCNTL, but can be overridden to SYS_FCNTL64.
+var FcntlSyscall uintptr = syscall.SYS_FCNTL
+
 func IsNonblock(fd int) (nonblocking bool, err error) {
-	flag, _, e1 := syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), uintptr(syscall.F_GETFL), 0)
+	flag, _, e1 := syscall.Syscall(FcntlSyscall, uintptr(fd), uintptr(syscall.F_GETFL), 0)
 	if e1 != 0 {
 		return false, e1
 	}
diff --git a/src/runtime/export_darwin_test.go b/src/runtime/export_darwin_test.go
new file mode 100644
index 0000000000..e9b6eb36da
--- /dev/null
+++ b/src/runtime/export_darwin_test.go
@@ -0,0 +1,13 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime
+
+func Fcntl(fd, cmd, arg uintptr) (uintptr, uintptr) {
+	r := fcntl(int32(fd), int32(cmd), int32(arg))
+	if r < 0 {
+		return ^uintptr(0), uintptr(-r)
+	}
+	return uintptr(r), 0
+}
diff --git a/src/runtime/nbpipe_fcntl_libc_test.go b/src/runtime/nbpipe_fcntl_libc_test.go
index 70f4b8348b..b38c58399b 100644
--- a/src/runtime/nbpipe_fcntl_libc_test.go
+++ b/src/runtime/nbpipe_fcntl_libc_test.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build aix solaris
+// +build aix darwin solaris
 
 package runtime_test
 
diff --git a/src/runtime/nbpipe_fcntl_unix_test.go b/src/runtime/nbpipe_fcntl_unix_test.go
index 06b3275f06..75acdb62dd 100644
--- a/src/runtime/nbpipe_fcntl_unix_test.go
+++ b/src/runtime/nbpipe_fcntl_unix_test.go
@@ -2,13 +2,16 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd linux netbsd openbsd
+// +build dragonfly freebsd linux netbsd openbsd
 
 package runtime_test
 
-import "syscall"
+import (
+	"internal/syscall/unix"
+	"syscall"
+)
 
 func fcntl(fd uintptr, cmd int, arg uintptr) (uintptr, syscall.Errno) {
-	res, _, err := syscall.Syscall(syscall.SYS_FCNTL, fd, uintptr(cmd), arg)
+	res, _, err := syscall.Syscall(unix.FcntlSyscall, fd, uintptr(cmd), arg)
 	return res, err
 }
diff --git a/src/syscall/flock_linux_32bit.go b/src/syscall/flock_linux_32bit.go
index e1548995b2..e11aed6ed1 100644
--- a/src/syscall/flock_linux_32bit.go
+++ b/src/syscall/flock_linux_32bit.go
@@ -1,9 +1,12 @@
-// +build linux,386 linux,arm linux,mips linux,mipsle
-
 // Copyright 2014 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// If you change the build tags here, see
+// internal/syscall/unix/fcntl_linux_32bit.go.
+
+// +build linux,386 linux,arm linux,mips linux,mipsle
+
 package syscall
 
 func init() {