Iffileexists use on root

Function .onVerifyInstDir
;Check for program installation
IfFileExists $INSTDIR\bin\myprog.exe Good
Abort
Good:
FunctionEnd


ok this procedure works great if the bin\myprog.exe exits in a folder they select such as F:\apps\bin\myprog.exe but if bin\myprog.exe is right on the root of F:\ (f:\bin\myprog.exe) its not detected.

IS there a way to get this to work or am i not doing something right?

Thanks