diff --git a/src/backend/libc/thread/syscalls.rs b/src/backend/libc/thread/syscalls.rs
index 9198a7fbe..13b291d81 100644
--- a/src/backend/libc/thread/syscalls.rs
+++ b/src/backend/libc/thread/syscalls.rs
@@ -398,9 +398,9 @@ pub(crate) fn setuid_thread(uid: crate::ugid::Uid) -> io::Result<()> {
 #[cfg(linux_kernel)]
 #[inline]
 pub(crate) fn setresuid_thread(
-    ruid: crate::ugid::Uid,
-    euid: crate::ugid::Uid,
-    suid: crate::ugid::Uid,
+    ruid: Option<crate::ugid::Uid>,
+    euid: Option<crate::ugid::Uid>,
+    suid: Option<crate::ugid::Uid>,
 ) -> io::Result<()> {
     #[cfg(any(target_arch = "x86", target_arch = "arm", target_arch = "sparc"))]
     const SYS: c::c_long = c::SYS_setresuid32 as c::c_long;
@@ -411,7 +411,13 @@ pub(crate) fn setresuid_thread(
         fn setresuid(ruid: c::uid_t, euid: c::uid_t, suid: c::uid_t) via SYS -> c::c_int
     }
 
-    unsafe { ret(setresuid(ruid.as_raw(), euid.as_raw(), suid.as_raw())) }
+    unsafe {
+        ret(setresuid(
+            ruid.map_or(-1_i32 as u32, |x| x.as_raw()),
+            euid.map_or(-1_i32 as u32, |x| x.as_raw()),
+            suid.map_or(-1_i32 as u32, |x| x.as_raw()),
+        ))
+    }
 }
 
 #[cfg(linux_kernel)]
@@ -427,9 +433,9 @@ pub(crate) fn setgid_thread(gid: crate::ugid::Gid) -> io::Result<()> {
 #[cfg(linux_kernel)]
 #[inline]
 pub(crate) fn setresgid_thread(
-    rgid: crate::ugid::Gid,
-    egid: crate::ugid::Gid,
-    sgid: crate::ugid::Gid,
+    rgid: Option<crate::ugid::Gid>,
+    egid: Option<crate::ugid::Gid>,
+    sgid: Option<crate::ugid::Gid>,
 ) -> io::Result<()> {
     #[cfg(any(target_arch = "x86", target_arch = "arm", target_arch = "sparc"))]
     const SYS: c::c_long = c::SYS_setresgid32 as c::c_long;
@@ -440,7 +446,13 @@ pub(crate) fn setresgid_thread(
         fn setresgid(rgid: c::gid_t, egid: c::gid_t, sgid: c::gid_t) via SYS -> c::c_int
     }
 
-    unsafe { ret(setresgid(rgid.as_raw(), egid.as_raw(), sgid.as_raw())) }
+    unsafe {
+        ret(setresgid(
+            rgid.map_or(-1_i32 as u32, |x| x.as_raw()),
+            egid.map_or(-1_i32 as u32, |x| x.as_raw()),
+            sgid.map_or(-1_i32 as u32, |x| x.as_raw()),
+        ))
+    }
 }
 
 /// # Safety
diff --git a/src/backend/linux_raw/conv.rs b/src/backend/linux_raw/conv.rs
index 901451ae6..3d4693fe1 100644
--- a/src/backend/linux_raw/conv.rs
+++ b/src/backend/linux_raw/conv.rs
@@ -842,6 +842,14 @@ impl<'a, Num: ArgNumber> From<crate::ugid::Uid> for ArgReg<'a, Num> {
     }
 }
 
+#[cfg(feature = "thread")]
+impl<'a, Num: ArgNumber> From<Option<crate::ugid::Uid>> for ArgReg<'a, Num> {
+    #[inline]
+    fn from(t: Option<crate::ugid::Uid>) -> Self {
+        c_uint(t.map_or(-1_i32 as u32, |x| x.as_raw()))
+    }
+}
+
 #[cfg(any(feature = "process", feature = "thread"))]
 impl<'a, Num: ArgNumber> From<crate::ugid::Gid> for ArgReg<'a, Num> {
     #[inline]
@@ -850,6 +858,14 @@ impl<'a, Num: ArgNumber> From<crate::ugid::Gid> for ArgReg<'a, Num> {
     }
 }
 
+#[cfg(feature = "thread")]
+impl<'a, Num: ArgNumber> From<Option<crate::ugid::Gid>> for ArgReg<'a, Num> {
+    #[inline]
+    fn from(t: Option<crate::ugid::Gid>) -> Self {
+        c_uint(t.map_or(-1_i32 as u32, |x| x.as_raw()))
+    }
+}
+
 #[cfg(feature = "runtime")]
 impl<'a, Num: ArgNumber> From<crate::runtime::How> for ArgReg<'a, Num> {
     #[inline]
diff --git a/src/backend/linux_raw/thread/syscalls.rs b/src/backend/linux_raw/thread/syscalls.rs
index 352e06150..c9dc7751c 100644
--- a/src/backend/linux_raw/thread/syscalls.rs
+++ b/src/backend/linux_raw/thread/syscalls.rs
@@ -405,9 +405,9 @@ pub(crate) fn setuid_thread(uid: crate::ugid::Uid) -> io::Result<()> {
 
 #[inline]
 pub(crate) fn setresuid_thread(
-    ruid: crate::ugid::Uid,
-    euid: crate::ugid::Uid,
-    suid: crate::ugid::Uid,
+    ruid: Option<crate::ugid::Uid>,
+    euid: Option<crate::ugid::Uid>,
+    suid: Option<crate::ugid::Uid>,
 ) -> io::Result<()> {
     #[cfg(any(target_arch = "x86", target_arch = "arm", target_arch = "sparc"))]
     unsafe {
@@ -426,9 +426,9 @@ pub(crate) fn setgid_thread(gid: crate::ugid::Gid) -> io::Result<()> {
 
 #[inline]
 pub(crate) fn setresgid_thread(
-    rgid: crate::ugid::Gid,
-    egid: crate::ugid::Gid,
-    sgid: crate::ugid::Gid,
+    rgid: Option<crate::ugid::Gid>,
+    egid: Option<crate::ugid::Gid>,
+    sgid: Option<crate::ugid::Gid>,
 ) -> io::Result<()> {
     #[cfg(any(target_arch = "x86", target_arch = "arm", target_arch = "sparc"))]
     unsafe {
diff --git a/src/thread/id.rs b/src/thread/id.rs
index aa67c9eaa..a299628f3 100644
--- a/src/thread/id.rs
+++ b/src/thread/id.rs
@@ -105,8 +105,13 @@ pub fn set_thread_uid(uid: Uid) -> io::Result<()> {
 /// [Linux]: https://man7.org/linux/man-pages/man2/setresuid.2.html
 /// [linux_notes]: https://man7.org/linux/man-pages/man2/setresuid.2.html#NOTES
 #[inline]
-pub fn set_thread_res_uid(ruid: Uid, euid: Uid, suid: Uid) -> io::Result<()> {
-    backend::thread::syscalls::setresuid_thread(ruid, euid, suid)
+pub fn set_thread_res_uid<R, E, S>(ruid: R, euid: E, suid: S) -> io::Result<()>
+where
+    R: Into<Option<Uid>>,
+    E: Into<Option<Uid>>,
+    S: Into<Option<Uid>>,
+{
+    backend::thread::syscalls::setresuid_thread(ruid.into(), euid.into(), suid.into())
 }
 
 /// `setgid(gid)`—Sets the effective group ID of the current thread.
@@ -154,8 +159,13 @@ pub fn set_thread_gid(gid: Gid) -> io::Result<()> {
 /// [Linux]: https://man7.org/linux/man-pages/man2/setresgid.2.html
 /// [linux_notes]: https://man7.org/linux/man-pages/man2/setresgid.2.html#NOTES
 #[inline]
-pub fn set_thread_res_gid(rgid: Gid, egid: Gid, sgid: Gid) -> io::Result<()> {
-    backend::thread::syscalls::setresgid_thread(rgid, egid, sgid)
+pub fn set_thread_res_gid<R, E, S>(rgid: R, egid: E, sgid: S) -> io::Result<()>
+where
+    R: Into<Option<Gid>>,
+    E: Into<Option<Gid>>,
+    S: Into<Option<Gid>>,
+{
+    backend::thread::syscalls::setresgid_thread(rgid.into(), egid.into(), sgid.into())
 }
 
 /// `setgroups(groups)`—Sets the supplementary group IDs for the calling