diff --git a/dlls/msgsm32.acm/msgsm32.c b/dlls/msgsm32.acm/msgsm32.c
index 99eef9624ea..cbf396f3b46 100644
--- a/dlls/msgsm32.acm/msgsm32.c
+++ b/dlls/msgsm32.acm/msgsm32.c
@@ -125,13 +125,13 @@ static	LRESULT GSM_DriverDetails(PACMDRIVERDETAILSW add)
     add->cFilterTags = 0;
     add->hicon = NULL;
     MultiByteToWideChar( CP_ACP, 0, "Microsoft GSM 6.10", -1,
-                         add->szShortName, sizeof(add->szShortName)/sizeof(WCHAR) );
+                         add->szShortName, ARRAY_SIZE( add->szShortName ));
     MultiByteToWideChar( CP_ACP, 0, "Wine GSM 6.10 libgsm codec", -1,
-                         add->szLongName, sizeof(add->szLongName)/sizeof(WCHAR) );
+                         add->szLongName, ARRAY_SIZE( add->szLongName ));
     MultiByteToWideChar( CP_ACP, 0, "Brought to you by the Wine team...", -1,
-                         add->szCopyright, sizeof(add->szCopyright)/sizeof(WCHAR) );
+                         add->szCopyright, ARRAY_SIZE( add->szCopyright ));
     MultiByteToWideChar( CP_ACP, 0, "Refer to LICENSE file", -1,
-                         add->szLicensing, sizeof(add->szLicensing)/sizeof(WCHAR) );
+                         add->szLicensing, ARRAY_SIZE( add->szLicensing ));
     add->szFeatures[0] = 0;
     return MMSYSERR_NOERROR;
 }