diff --git a/unix/mmap_unix_test.go b/unix/mmap_unix_test.go
index a60a0f62..eb146059 100644
--- a/unix/mmap_unix_test.go
+++ b/unix/mmap_unix_test.go
@@ -9,6 +9,7 @@ package unix_test
 import (
 	"runtime"
 	"testing"
+	"unsafe"
 
 	"golang.org/x/sys/unix"
 )
@@ -49,3 +50,25 @@ func TestMmap(t *testing.T) {
 		t.Fatalf("Munmap: %v", err)
 	}
 }
+
+func TestMmapPtr(t *testing.T) {
+	mmapProt := unix.PROT_NONE
+	mmapPtrProt := unix.PROT_READ | unix.PROT_WRITE
+	b, err := unix.Mmap(-1, 0, 2*unix.Getpagesize(), mmapProt, unix.MAP_ANON|unix.MAP_PRIVATE)
+	if err != nil {
+		t.Fatalf("Mmap: %v", err)
+	}
+	if _, err := unix.MmapPtr(-1, 0, unsafe.Pointer(&b[0]), uintptr(unix.Getpagesize()),
+		mmapPtrProt, unix.MAP_ANON|unix.MAP_PRIVATE|unix.MAP_FIXED); err != nil {
+		t.Fatalf("MmapPtr: %v", err)
+	}
+
+	b[0] = 42
+
+	if err := unix.MunmapPtr(unsafe.Pointer(&b[0]), uintptr(unix.Getpagesize())); err != nil {
+		t.Fatalf("MunmapPtr: %v", err)
+	}
+	if err := unix.Munmap(b); err != nil {
+		t.Fatalf("Munmap: %v", err)
+	}
+}
diff --git a/unix/mremap_test.go b/unix/mremap_test.go
index e84104fc..5019dd78 100644
--- a/unix/mremap_test.go
+++ b/unix/mremap_test.go
@@ -8,6 +8,7 @@ package unix_test
 
 import (
 	"testing"
+	"unsafe"
 
 	"golang.org/x/sys/unix"
 )
@@ -44,3 +45,32 @@ func TestMremap(t *testing.T) {
 		t.Fatalf("remapping to a fixed address; got %v, want %v", err, unix.EINVAL)
 	}
 }
+
+func TestMremapPtr(t *testing.T) {
+	mmapProt := unix.PROT_NONE
+	mmapPtrProt := unix.PROT_READ | unix.PROT_WRITE
+	b, err := unix.Mmap(-1, 0, 2*unix.Getpagesize(), mmapProt, unix.MAP_ANON|unix.MAP_PRIVATE)
+	if err != nil {
+		t.Fatalf("Mmap: %v", err)
+	}
+	if _, err := unix.MmapPtr(-1, 0, unsafe.Pointer(&b[0]), uintptr(unix.Getpagesize()),
+		mmapPtrProt, unix.MAP_ANON|unix.MAP_PRIVATE|unix.MAP_FIXED); err != nil {
+		t.Fatalf("MmapPtr: %v", err)
+	}
+
+	b[0] = 42
+
+	if _, err := unix.MremapPtr(
+		unsafe.Pointer(&b[0]), uintptr(unix.Getpagesize()),
+		unsafe.Pointer(&b[unix.Getpagesize()]), uintptr(unix.Getpagesize()),
+		unix.MremapFixed|unix.MremapMaymove); err != nil {
+		t.Fatalf("MremapPtr: %v", err)
+	}
+	if got := b[unix.Getpagesize()]; got != 42 {
+		t.Errorf("got %d, want 42", got)
+	}
+
+	if err := unix.Munmap(b); err != nil {
+		t.Fatalf("Munmap: %v", err)
+	}
+}
diff --git a/unix/syscall_unix.go b/unix/syscall_unix.go
index 88909f13..4e92e5aa 100644
--- a/unix/syscall_unix.go
+++ b/unix/syscall_unix.go
@@ -154,7 +154,7 @@ func Munmap(b []byte) (err error) {
 	return mapper.Munmap(b)
 }
 
-func MmapPtr(addr unsafe.Pointer, length uintptr, prot int, flags int, fd int, offset int64) (ret unsafe.Pointer, err error) {
+func MmapPtr(fd int, offset int64, addr unsafe.Pointer, length uintptr, prot int, flags int) (ret unsafe.Pointer, err error) {
 	xaddr, err := mapper.mmap(uintptr(addr), length, prot, flags, fd, offset)
 	return unsafe.Pointer(xaddr), err
 }