diff --git a/unix/mmap_unix_test.go b/unix/mmap_unix_test.go
index eb146059c..d5f4db037 100644
--- a/unix/mmap_unix_test.go
+++ b/unix/mmap_unix_test.go
@@ -9,7 +9,6 @@ package unix_test
 import (
 	"runtime"
 	"testing"
-	"unsafe"
 
 	"golang.org/x/sys/unix"
 )
@@ -52,23 +51,20 @@ func TestMmap(t *testing.T) {
 }
 
 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)
+	p, err := unix.MmapPtr(-1, 0, nil, uintptr(2*unix.Getpagesize()),
+		unix.PROT_NONE, unix.MAP_ANON|unix.MAP_PRIVATE)
 	if err != nil {
-		t.Fatalf("Mmap: %v", err)
+		t.Fatalf("MmapPtr: %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 {
+
+	if _, err := unix.MmapPtr(-1, 0, p, uintptr(unix.Getpagesize()),
+		unix.PROT_READ|unix.PROT_WRITE, unix.MAP_ANON|unix.MAP_PRIVATE|unix.MAP_FIXED); err != nil {
 		t.Fatalf("MmapPtr: %v", err)
 	}
 
-	b[0] = 42
+	*(*byte)(p) = 42
 
-	if err := unix.MunmapPtr(unsafe.Pointer(&b[0]), uintptr(unix.Getpagesize())); err != nil {
+	if err := unix.MunmapPtr(p, uintptr(2*unix.Getpagesize())); err != nil {
 		t.Fatalf("MunmapPtr: %v", err)
 	}
-	if err := unix.Munmap(b); err != nil {
-		t.Fatalf("Munmap: %v", err)
-	}
 }