diff --git a/minix/commands/swifi/systest.c b/minix/commands/swifi/systest.c
index f45967228..e0a7234dd 100644
--- a/minix/commands/swifi/systest.c
+++ b/minix/commands/swifi/systest.c
@@ -73,7 +73,7 @@ main(int argc, char * argv[])
     goto Cleanup;
   }
 
-  memset(res, 0, sizeof(ressize));
+  memset(res, 0, ressize);
 
   /*
   // Find out where the faults will be injected