diff --git a/src/threads.h b/src/threads.h
index 74c32c90033fc511661ab765d464c69e4ef0795b..a4c6b961a9191532f2a8e64c1cb53f216165c5aa 100644
--- a/src/threads.h
+++ b/src/threads.h
@@ -259,7 +259,7 @@ struct thread_state {
 #endif
 
 #ifndef th_hash
-#define th_hash(X) hashmem(&(X),sizeof(THREAD_T), 16)
+#define th_hash(X) hashmem((unsigned char *)&(X),sizeof(THREAD_T), 16)
 #endif
 
 /* Define to get a debug-trace of some of the threads operations. */