diff --git a/lib/std/os/windows.zig b/lib/std/os/windows.zig
index 4249205a346625a3dbf7380d8a5038cfa7068979..346eab7915ef5c70e5910a1235cd08afaaab28fb 100644
--- a/lib/std/os/windows.zig
+++ b/lib/std/os/windows.zig
@@ -132,6 +132,7 @@ pub fn DeviceIoControl(
         overlapped,
     ) == 0) {
         switch (kernel32.GetLastError()) {
+            ERROR.IO_PENDING => if (overlapped == null) unreachable,
             else => |err| return unexpectedError(err),
         }
     }
diff --git a/lib/std/os/windows/kernel32.zig b/lib/std/os/windows/kernel32.zig
index 82dd03b82942113258a393aee7b3c3d86f1d64a7..954261bd1b406fa143b900b713379280dab94a5b 100644
--- a/lib/std/os/windows/kernel32.zig
+++ b/lib/std/os/windows/kernel32.zig
@@ -59,7 +59,7 @@ pub extern "kernel32" stdcallcc fn DeviceIoControl(
     nInBufferSize: DWORD,
     lpOutBuffer: ?LPVOID,
     nOutBufferSize: DWORD,
-    lpBytesReturned: LPDWORD,
+    lpBytesReturned: ?*DWORD,
     lpOverlapped: ?*OVERLAPPED,
 ) BOOL;