diff --git a/std/os/windows/kernel32.zig b/std/os/windows/kernel32.zig
index 8fd351c12..7a6126133 100644
--- a/std/os/windows/kernel32.zig
+++ b/std/os/windows/kernel32.zig
@@ -259,7 +259,7 @@ pub extern "kernel32" stdcallcc fn InitOnceExecuteOnce(InitOnce: *RTL_RUN_ONCE,
 pub const PINIT_ONCE_FN = ?extern fn(InitOnce: *RTL_RUN_ONCE, Parameter: ?PVOID, Context: ?PVOID) BOOL;
 
 pub const RTL_RUN_ONCE = extern struct {
-    Ptr: PVOID,
+    Ptr: ?PVOID,
 };
 
 pub const INIT_ONCE_STATIC_INIT = RTL_RUN_ONCE {