diff --git a/Source/Windows/Common/WinAPI/Sync.cpp b/Source/Windows/Common/WinAPI/Sync.cpp
index 88047a4c7..62a684c30 100644
--- a/Source/Windows/Common/WinAPI/Sync.cpp
+++ b/Source/Windows/Common/WinAPI/Sync.cpp
@@ -133,5 +133,8 @@ DLLEXPORT_FUNC(WINBOOL, SwitchToThread, ()) {
 }
 
 DLLEXPORT_FUNC(void, Sleep, (DWORD dwMilliseconds)) {
-  UNIMPLEMENTED();
+  LARGE_INTEGER Time;
+  // A negative value indicates a relative time measured in 100ns intervals.
+  Time.QuadPart = static_cast<ULONGLONG>(dwMilliseconds) * -10000;
+  NtDelayExecution(false, &Time);
 }
diff --git a/Source/Windows/include/winternl.h b/Source/Windows/include/winternl.h
index efd211c5a..686cc0036 100644
--- a/Source/Windows/include/winternl.h
+++ b/Source/Windows/include/winternl.h
@@ -497,6 +497,7 @@ NTSTATUS WINAPI NtAllocateVirtualMemoryEx(HANDLE, PVOID*, SIZE_T*, ULONG, ULONG,
 NTSTATUS WINAPI NtAllocateVirtualMemory(HANDLE, PVOID*, ULONG_PTR, SIZE_T*, ULONG, ULONG);
 NTSTATUS WINAPI NtContinue(PCONTEXT, BOOLEAN);
 NTSTATUS WINAPI NtCreateSection(HANDLE*, ACCESS_MASK, const OBJECT_ATTRIBUTES*, const LARGE_INTEGER*, ULONG, ULONG, HANDLE);
+NTSTATUS WINAPI NtDelayExecution(BOOLEAN, const LARGE_INTEGER*);
 NTSTATUS WINAPI NtDuplicateObject(HANDLE, HANDLE, HANDLE, PHANDLE, ACCESS_MASK, ULONG, ULONG);
 NTSTATUS WINAPI NtFlushInstructionCache(HANDLE, LPCVOID, SIZE_T);
 NTSTATUS WINAPI NtFreeVirtualMemory(HANDLE, PVOID*, SIZE_T*, ULONG);