diff --git a/src/pkg/os/os_test.go b/src/pkg/os/os_test.go
index 4c9feab1ceb..65475c118ae 100644
--- a/src/pkg/os/os_test.go
+++ b/src/pkg/os/os_test.go
@@ -567,8 +567,8 @@ func checkSize(t *testing.T, f *File, size int64) {
 	}
 }
 
-func TestTruncate(t *testing.T) {
-	f := newFile("TestTruncate", t)
+func TestFTruncate(t *testing.T) {
+	f := newFile("TestFTruncate", t)
 	defer Remove(f.Name())
 	defer f.Close()
 
@@ -585,6 +585,24 @@ func TestTruncate(t *testing.T) {
 	checkSize(t, f, 13+9) // wrote at offset past where hello, world was.
 }
 
+func TestTruncate(t *testing.T) {
+	f := newFile("TestTruncate", t)
+	defer Remove(f.Name())
+	defer f.Close()
+
+	checkSize(t, f, 0)
+	f.Write([]byte("hello, world\n"))
+	checkSize(t, f, 13)
+	Truncate(f.Name(), 10)
+	checkSize(t, f, 10)
+	Truncate(f.Name(), 1024)
+	checkSize(t, f, 1024)
+	Truncate(f.Name(), 0)
+	checkSize(t, f, 0)
+	f.Write([]byte("surprise!"))
+	checkSize(t, f, 13+9) // wrote at offset past where hello, world was.
+}
+
 // Use TempDir() to make sure we're on a local file system,
 // so that timings are not distorted by latency and caching.
 // On NFS, timings can be off due to caching of meta-data on
diff --git a/src/pkg/syscall/syscall_linux_arm.go b/src/pkg/syscall/syscall_linux_arm.go
index 6472c4db54f..45874588594 100644
--- a/src/pkg/syscall/syscall_linux_arm.go
+++ b/src/pkg/syscall/syscall_linux_arm.go
@@ -24,7 +24,6 @@ func NsecToTimeval(nsec int64) (tv Timeval) {
 }
 
 // Pread and Pwrite are special: they insert padding before the int64.
-// (Ftruncate and truncate are not; go figure.)
 
 func Pread(fd int, p []byte, offset int64) (n int, errno int) {
 	var _p0 unsafe.Pointer
@@ -48,6 +47,20 @@ func Pwrite(fd int, p []byte, offset int64) (n int, errno int) {
 	return
 }
 
+func Ftruncate(fd int, length int64) (errno int) {
+	// ARM EABI requires 64-bit arguments should be put in a pair
+	// of registers from an even register number.
+	_, _, e1 := Syscall6(SYS_FTRUNCATE64, uintptr(fd), 0, uintptr(length), uintptr(length>>32), 0, 0)
+	errno = int(e1)
+	return
+}
+
+func Truncate(path string, length int64) (errno int) {
+	_, _, e1 := Syscall6(SYS_TRUNCATE64, uintptr(unsafe.Pointer(StringBytePtr(path))), 0, uintptr(length), uintptr(length>>32), 0, 0)
+	errno = int(e1)
+	return
+}
+
 // Seek is defined in assembly.
 
 func Seek(fd int, offset int64, whence int) (newoffset int64, errno int)
@@ -72,7 +85,6 @@ func Seek(fd int, offset int64, whence int) (newoffset int64, errno int)
 //sys	Fchown(fd int, uid int, gid int) (errno int)
 //sys	Fstat(fd int, stat *Stat_t) (errno int) = SYS_FSTAT64
 //sys	Fstatfs(fd int, buf *Statfs_t) (errno int) = SYS_FSTATFS64
-//sys	Ftruncate(fd int, length int64) (errno int) = SYS_FTRUNCATE64
 //sysnb	Getegid() (egid int)
 //sysnb	Geteuid() (euid int)
 //sysnb	Getgid() (gid int)
@@ -92,7 +104,6 @@ func Seek(fd int, offset int64, whence int) (newoffset int64, errno int)
 //sys	Splice(rfd int, roff *int64, wfd int, woff *int64, len int, flags int) (n int, errno int)
 //sys	Stat(path string, stat *Stat_t) (errno int) = SYS_STAT64
 //sys	Statfs(path string, buf *Statfs_t) (errno int) = SYS_STATFS64
-//sys	Truncate(path string, length int64) (errno int) = SYS_TRUNCATE64
 
 // Vsyscalls on amd64.
 //sysnb	Gettimeofday(tv *Timeval) (errno int)
diff --git a/src/pkg/syscall/zsyscall_linux_arm.go b/src/pkg/syscall/zsyscall_linux_arm.go
index 43b84d98c5d..f41240d5c46 100644
--- a/src/pkg/syscall/zsyscall_linux_arm.go
+++ b/src/pkg/syscall/zsyscall_linux_arm.go
@@ -970,14 +970,6 @@ func Fstatfs(fd int, buf *Statfs_t) (errno int) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Ftruncate(fd int, length int64) (errno int) {
-	_, _, e1 := Syscall(SYS_FTRUNCATE64, uintptr(fd), uintptr(length>>32), uintptr(length))
-	errno = int(e1)
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Getegid() (egid int) {
 	r0, _, _ := RawSyscall(SYS_GETEGID, 0, 0, 0)
 	egid = int(r0)
@@ -1132,14 +1124,6 @@ func Statfs(path string, buf *Statfs_t) (errno int) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
-func Truncate(path string, length int64) (errno int) {
-	_, _, e1 := Syscall(SYS_TRUNCATE64, uintptr(unsafe.Pointer(StringBytePtr(path))), uintptr(length>>32), uintptr(length))
-	errno = int(e1)
-	return
-}
-
-// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
-
 func Gettimeofday(tv *Timeval) (errno int) {
 	_, _, e1 := RawSyscall(SYS_GETTIMEOFDAY, uintptr(unsafe.Pointer(tv)), 0, 0)
 	errno = int(e1)