diff --git a/src/header/signal/mod.rs b/src/header/signal/mod.rs
--- a/src/header/signal/mod.rs
+++ b/src/header/signal/mod.rs
@@ -2,7 +2,10 @@
 //!
 //! See <https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/signal.h.html>.
 
-use core::{mem, ptr};
+use core::{
+    mem, ptr,
+    sync::atomic::Ordering,
+};
 
 use cbitset::BitSet;
 
@@ -157,10 +160,17 @@
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/pthread_kill.html>.
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn pthread_kill(thread: pthread_t, sig: c_int) -> c_int {
-    let os_tid = {
-        let pthread = unsafe { &*(thread as *const crate::pthread::Pthread) };
-        unsafe { pthread.os_tid.get().read() }
-    };
+    let pthread = unsafe { &*(thread as *const crate::pthread::Pthread) };
+    let os_tid = unsafe { pthread.os_tid.get().read() };
+    let flags = crate::pthread::PthreadFlags::from_bits_retain(
+        pthread.flags.load(Ordering::Acquire),
+    );
+    if flags.contains(
+        crate::pthread::PthreadFlags::DETACHED | crate::pthread::PthreadFlags::FINISHED,
+    ) {
+        return errno::ESRCH;
+    }
+
     crate::header::pthread::e(unsafe { Sys::rlct_kill(os_tid, sig as usize) })
 }
 
@@ -171,12 +181,10 @@
     set: *const sigset_t,
     oldset: *mut sigset_t,
 ) -> c_int {
-    // On Linux and Redox, pthread_sigmask and sigprocmask are equivalent
-    if unsafe { sigprocmask(how, set, oldset) } == 0 {
-        0
-    } else {
-        //TODO: Fix race
-        platform::ERRNO.get()
+    let result = unsafe { Sys::sigprocmask(how, set.as_ref(), oldset.as_mut()) };
+    match result {
+        Ok(()) => 0,
+        Err(errno) => errno.0,
     }
 }
 
diff --git a/src/pthread/mod.rs b/src/pthread/mod.rs
--- a/src/pthread/mod.rs
+++ b/src/pthread/mod.rs
@@ -31,6 +31,7 @@
         stack_size: 0,
 
         os_tid: UnsafeCell::new(Sys::current_os_tid()),
+        robust_list_head: UnsafeCell::new(ptr::null_mut()),
     };
 
     #[cfg(target_os = "redox")]
@@ -60,6 +61,7 @@
 bitflags::bitflags! {
     pub struct PthreadFlags: usize {
         const DETACHED = 1;
+        const FINISHED = 1 << 1;
     }
 }
 
@@ -306,7 +308,9 @@
 
     unsafe { crate::sync::pthread_mutex::mark_robust_mutexes_dead(this) };
 
-    if this.flags.load(Ordering::Acquire) & PthreadFlags::DETACHED.bits() != 0 {
+    let flags = this.flags.fetch_or(PthreadFlags::FINISHED.bits(), Ordering::AcqRel);
+
+    if flags & PthreadFlags::DETACHED.bits() != 0 {
         unsafe { dealloc_thread(this) };
     } else {
         unsafe { this.waitval.post(retval) };
diff --git a/src/ld_so/tcb.rs b/src/ld_so/tcb.rs
--- a/src/ld_so/tcb.rs
+++ b/src/ld_so/tcb.rs
@@ -107,6 +107,7 @@
                     stack_base: core::ptr::null_mut(),
                     stack_size: 0,
                     os_tid: UnsafeCell::new(OsTid::default()),
+                    robust_list_head: UnsafeCell::new(ptr::null_mut()),
                 },
 
                 dtv_ptr: ptr::null_mut(),