diff --git a/core/libs/prx/libkernel/System/src/Signals.cpp b/core/libs/prx/libkernel/System/src/Signals.cpp
index 35bfc4e4b..0ce268890 100644
--- a/core/libs/prx/libkernel/System/src/Signals.cpp
+++ b/core/libs/prx/libkernel/System/src/Signals.cpp
@@ -1,5 +1,6 @@
 #include "SceTypes.hpp"
 #include "prx/libc/include/General.hpp"
+#include "prx/libkernel/Pthread/Posix/Common.hpp"
 #include "prx/libc/include/general/VabiMacros.hpp"
 #include <atomic>
 #include <chrono>
@@ -203,8 +204,8 @@ int APS5_VABI kill_nid_postfix(int pid, int guest) {
     return guest == 0 ? 0 : raise_nid_postfix(guest);
 }
 int APS5_VABI pthread_kill_nid_postfix(Pthread thread, int guest) {
-    if (guest < 0 || guest > MaxSignal) return 22;
-    if (thread == nullptr) return 3;
+    if (guest < 0 || guest > MaxSignal) return PosixThread::GUEST_EINVAL;
+    if (thread == nullptr) return PosixThread::GUEST_ESRCH;
     if (guest == 0) return 0;
     if (thread != scePthreadSelf()) NotImplemented_nid_no_patch(("pthread_kill signal " + std::to_string(guest) + " to another thread").c_str());
     return raise_nid_postfix(guest) == 0 ? 0 : *__error_nid_postfix();
diff --git a/core/libs/tests/GuestSignals.cpp b/core/libs/tests/GuestSignals.cpp
index 187e6ae36..0f048e414 100644
--- a/core/libs/tests/GuestSignals.cpp
+++ b/core/libs/tests/GuestSignals.cpp
@@ -58,6 +58,8 @@ int main() {
     Require(pthread_kill_nid_postfix(scePthreadSelf(), 200) == 22);
     Require(pthread_kill_nid_postfix(scePthreadSelf(), -1) == 22);
     Require(pthread_kill_nid_postfix(nullptr, 15) == 3);
+    Require(pthread_kill_nid_postfix(nullptr, 128) == 3);
+    Require(pthread_kill_nid_postfix(nullptr, 129) == 22);
     bool threw = false;
     try { pthread_kill_nid_postfix(reinterpret_cast<void*>(std::uintptr_t{0x10}), 15); }
     catch (const std::runtime_error&) { threw = true; }