diff --git a/reactos/base/applications/taskmgr/perfpage.c b/reactos/base/applications/taskmgr/perfpage.c
index 3ceadb56cdc..d37bc9e46b2 100644
--- a/reactos/base/applications/taskmgr/perfpage.c
+++ b/reactos/base/applications/taskmgr/perfpage.c
@@ -371,11 +371,11 @@ DWORD WINAPI PerformancePageRefreshThread(void *lpParameter)
 
             StrFormatByteSizeW(CommitChargeTotal * 1024,
                                szChargeTotalFormat,
-                               sizeof(szChargeTotalFormat));
+                               _countof(szChargeTotalFormat));
 
             StrFormatByteSizeW(CommitChargeLimit * 1024,
                                szChargeLimitFormat,
-                               sizeof(szChargeLimitFormat));
+                               _countof(szChargeLimitFormat));
 
             if (!bInMenuLoop)
             {