diff --git a/unix/mkpost.go b/unix/mkpost.go
index 4dc06923..6d263cf1 100644
--- a/unix/mkpost.go
+++ b/unix/mkpost.go
@@ -46,6 +46,10 @@ func main() {
 	valRegex := regexp.MustCompile(`type (Fsid|Sigset_t) struct {(\s+)X__val(\s+\S+\s+)}`)
 	b = valRegex.ReplaceAll(b, []byte("type $1 struct {${2}Val$3}"))
 
+	// Intentionally export __fds_bits field in FdSet
+	fdSetRegex := regexp.MustCompile(`type (FdSet) struct {(\s+)X__fds_bits(\s+\S+\s+)}`)
+	b = fdSetRegex.ReplaceAll(b, []byte("type $1 struct {${2}Bits$3}"))
+
 	// If we have empty Ptrace structs, we should delete them. Only s390x emits
 	// nonempty Ptrace structs.
 	ptraceRexexp := regexp.MustCompile(`type Ptrace((Psw|Fpregs|Per) struct {\s*})`)
diff --git a/unix/ztypes_freebsd_386.go b/unix/ztypes_freebsd_386.go
index 28ef5242..c146c1ad 100644
--- a/unix/ztypes_freebsd_386.go
+++ b/unix/ztypes_freebsd_386.go
@@ -339,7 +339,7 @@ type Kevent_t struct {
 }
 
 type FdSet struct {
-	_ [32]uint32
+	Bits [32]uint32
 }
 
 const (
diff --git a/unix/ztypes_freebsd_amd64.go b/unix/ztypes_freebsd_amd64.go
index e2d984a4..ac33a8dd 100644
--- a/unix/ztypes_freebsd_amd64.go
+++ b/unix/ztypes_freebsd_amd64.go
@@ -337,7 +337,7 @@ type Kevent_t struct {
 }
 
 type FdSet struct {
-	_ [16]uint64
+	Bits [16]uint64
 }
 
 const (
diff --git a/unix/ztypes_freebsd_arm.go b/unix/ztypes_freebsd_arm.go
index 9b415aba..e27511a6 100644
--- a/unix/ztypes_freebsd_arm.go
+++ b/unix/ztypes_freebsd_arm.go
@@ -337,7 +337,7 @@ type Kevent_t struct {
 }
 
 type FdSet struct {
-	_ [32]uint32
+	Bits [32]uint32
 }
 
 const (