diff --git a/code/thw3.c b/code/thw3.c
index dd573df14c..deff280919 100644
--- a/code/thw3.c
+++ b/code/thw3.c
@@ -259,7 +259,7 @@ Res ThreadDescribe(Thread thread, mps_lib_FILE *stream, Count depth)
 }
 
 
-Res ThreadScan(ScanState ss, Thread thread, Word *stackCold,
+Res ThreadScan(ScanState ss, Thread thread, void *stackCold,
                mps_area_scan_t scan_area, void *closure)
 {
   DWORD id;