diff --git a/sys/src/9/pc64/mem.h b/sys/src/9/pc64/mem.h
index 9ec07363a..acbbff43d 100644
--- a/sys/src/9/pc64/mem.h
+++ b/sys/src/9/pc64/mem.h
@@ -36,7 +36,7 @@
  * Time
  */
 #define HZ		(100)			/* clock frequency */
-#define MS2HZ		(100/HZ)		/* millisec per clock tick */
+#define MS2HZ		(1000/HZ)		/* millisec per clock tick */
 #define TK2SEC(t)	((t)/HZ)		/* ticks to seconds */
 
 /*