diff --git a/core/libs/prx/libc/CMakeLists.txt b/core/libs/prx/libc/CMakeLists.txt
index f5736578e..847b8ffc3 100644
--- a/core/libs/prx/libc/CMakeLists.txt
+++ b/core/libs/prx/libc/CMakeLists.txt
@@ -77,6 +77,16 @@ if(BUILD_TESTING)
         set_tests_properties(guest_math PROPERTIES ENVIRONMENT_MODIFICATION
             "PATH=path_list_prepend:$<TARGET_FILE_DIR:libc>")
     endif()
+    add_test_executable(guest_execute_once_tests ${LIBS_INCLUDE_DIR}/tests/GuestExecuteOnce.cpp)
+    target_include_directories(guest_execute_once_tests PRIVATE ${LIBS_INCLUDE_DIR})
+    target_link_libraries(guest_execute_once_tests PRIVATE libc)
+    configure_windows_unwind(guest_execute_once_tests)
+    add_test(NAME guest_execute_once COMMAND guest_execute_once_tests)
+    set_tests_properties(guest_execute_once PROPERTIES TIMEOUT 20)
+    if(WIN32)
+        set_tests_properties(guest_execute_once PROPERTIES ENVIRONMENT_MODIFICATION
+            "PATH=path_list_prepend:$<TARGET_FILE_DIR:libc>")
+    endif()
     add_test_executable(guest_working_directory_tests ${LIBS_INCLUDE_DIR}/tests/GuestWorkingDirectory.cpp)
     target_include_directories(guest_working_directory_tests PRIVATE ${LIBS_INCLUDE_DIR})
     target_link_libraries(guest_working_directory_tests PRIVATE libc)
diff --git a/core/libs/prx/libc/Export.cpp b/core/libs/prx/libc/Export.cpp
index 1d54d1084..bdb6ca001 100644
--- a/core/libs/prx/libc/Export.cpp
+++ b/core/libs/prx/libc/Export.cpp
@@ -55,12 +55,6 @@ int APS5_VABI libcCyberUnknown19(void) {
 }
 
 
-APS5_EXPORT("DiGVep5yB5w", libcCyberUnknown01);
-std::uint64_t APS5_VABI libcCyberUnknown01(void) {
-    NotImplemented_nid_no_patch("DiGVep5yB5w");
-    return 0;
-}
-
 APS5_EXPORT("Ye20uNnlglA", libcCyberUnknown02);
 std::uint64_t APS5_VABI libcCyberUnknown02(void) {
     NotImplemented_nid_no_patch("Ye20uNnlglA");
diff --git a/core/libs/prx/libc/src/CxxAbiSupport.cpp b/core/libs/prx/libc/src/CxxAbiSupport.cpp
index b3e467664..8f32a8572 100644
--- a/core/libs/prx/libc/src/CxxAbiSupport.cpp
+++ b/core/libs/prx/libc/src/CxxAbiSupport.cpp
@@ -16,6 +16,7 @@
 #include <locale>
 #include <regex>
 #include <functional>
+#include <mutex>
 
 #include "prx/libc/include/General.hpp"
 
@@ -40,4 +41,15 @@ int APS5_VABI LibcInternalExtCxaThreadAtexit_nid_postfix(void (*destructor)(void
 
 const std::error_category* _ZSt17iostream_categoryv_nid_postfix() { return &std::iostream_category(); }
 
+int APS5_VABI _ZSt13_Execute_onceRSt9once_flagPFiPvS1_PS1_ES1__nid_postfix(
+    int* flag, int (APS5_VABI *callback)(void*, void*, void**), void* arg
+) {
+    static std::recursive_mutex mutex;
+    std::lock_guard lock(mutex);
+    if (*flag != 0) return 1;
+    if (callback(nullptr, arg, nullptr) == 0) return 0;
+    *flag = 1;
+    return 1;
+}
+
 }
diff --git a/core/libs/tests/GuestExecuteOnce.cpp b/core/libs/tests/GuestExecuteOnce.cpp
new file mode 100644
index 000000000..327fbe8c3
--- /dev/null
+++ b/core/libs/tests/GuestExecuteOnce.cpp
@@ -0,0 +1,70 @@
+#include "prx/libc/include/general/VabiMacros.hpp"
+#include <array>
+#include <atomic>
+#include <cstdlib>
+#include <thread>
+
+using Callback = int (APS5_VABI *)(void*, void*, void**);
+extern "C" int APS5_VABI _ZSt13_Execute_onceRSt9once_flagPFiPvS1_PS1_ES1__nid_postfix(int*, Callback, void*);
+static int ExecuteOnce(int* flag, Callback callback, void* arg) {
+    return _ZSt13_Execute_onceRSt9once_flagPFiPvS1_PS1_ES1__nid_postfix(flag, callback, arg);
+}
+static void Require(bool value) { if (!value) std::abort(); }
+
+static std::atomic<int> calls{0}, arrived{0};
+static int control = 0, nested = 0, failing = 0, throwing = 0;
+static int published = 0, nestedValue = 0, failures = 0, throws = 0;
+static void* seenFirst = &control;
+static void* seenArg = nullptr;
+static void** seenThird = reinterpret_cast<void**>(&control);
+
+static int APS5_VABI Nested(void*, void* arg, void**) {
+    nestedValue = *static_cast<int*>(arg);
+    return 1;
+}
+static int APS5_VABI Initialize(void* first, void* arg, void** third) {
+    ++calls;
+    seenFirst = first;
+    seenArg = arg;
+    seenThird = third;
+    while (arrived.load() != 16) std::this_thread::yield();
+    int value = 17;
+    Require(ExecuteOnce(&nested, Nested, &value) == 1);
+    published = 42;
+    return 5;
+}
+static int APS5_VABI Fail(void*, void*, void**) {
+    ++failures;
+    return 0;
+}
+static int APS5_VABI Throw(void*, void*, void**) {
+    if (++throws == 1) throw 7;
+    return 1;
+}
+static int APS5_VABI Unreachable(void*, void*, void**) {
+    std::abort();
+}
+
+int main() {
+    int token = 0;
+    std::array<std::thread, 16> workers;
+    for (auto& worker : workers) worker = std::thread([&token] {
+        ++arrived;
+        Require(ExecuteOnce(&control, Initialize, &token) == 1);
+        Require(published == 42 && nestedValue == 17);
+    });
+    for (auto& worker : workers) worker.join();
+    Require(calls == 1 && control == 1 && nested == 1);
+    Require(seenFirst == nullptr && seenArg == &token && seenThird == nullptr);
+    Require(ExecuteOnce(&control, Unreachable, nullptr) == 1 && calls == 1);
+
+    Require(ExecuteOnce(&failing, Fail, nullptr) == 0 && failing == 0 && failures == 1);
+    Require(ExecuteOnce(&failing, Fail, nullptr) == 0 && failing == 0 && failures == 2);
+
+    try { ExecuteOnce(&throwing, Throw, nullptr); std::abort(); }
+    catch (int value) { Require(value == 7 && throwing == 0); }
+    Require(ExecuteOnce(&throwing, Throw, nullptr) == 1 && throwing == 1 && throws == 2);
+
+    int preset = -3;
+    Require(ExecuteOnce(&preset, Unreachable, nullptr) == 1 && preset == -3);
+}