diff --git a/dlls/ntdll/unix/file.c b/dlls/ntdll/unix/file.c
index c169b49343f..233778df3b2 100644
--- a/dlls/ntdll/unix/file.c
+++ b/dlls/ntdll/unix/file.c
@@ -1963,13 +1963,13 @@ static NTSTATUS get_mountmgr_fs_info( HANDLE handle, int fd, struct mountmgr_uni
     letter = find_dos_device( unix_name );
     free( unix_name );
 
+    memset( drive, 0, sizeof(*drive) );
     if (letter == -1)
     {
         struct stat st;
 
         fstat( fd, &st );
         drive->unix_dev = st.st_rdev ? st.st_rdev : st.st_dev;
-        drive->letter = 0;
     }
     else
         drive->letter = 'a' + letter;