diff --git a/zdump/zg.h b/zdump/zg.h
index dcab7c44..2229f23c 100644
--- a/zdump/zg.h
+++ b/zdump/zg.h
@@ -140,8 +140,8 @@ static inline u32 zg_csum_partial(const void *buf, int len, u32 sum)
 /*
  * Pointer atrithmetic
  */
-#define PTR_SUB(x, y) (((char *) (x)) - ((unsigned long) (y)))
-#define PTR_ADD(x, y) (((char *) (x)) + ((unsigned long) (y)))
+#define PTR_SUB(x, y) ((void *)(((char *) (x)) - ((unsigned long) (y))))
+#define PTR_ADD(x, y) ((void *)(((char *) (x)) + ((unsigned long) (y))))
 #define PTR_DIFF(x, y) ((unsigned long)PTR_SUB(x, y))
 
 /*