Incompatibility between MnSymbol and unicode-math?

The following code

\documentclass{minimal}

\usepackage{MnSymbol,unicode-math}

\begin{document}

$A\bar\smalltriangleup B$

\end{document}


results in

!Internal error: bad native font flag in map_char_to_glyph'
`

with no output at all.

I need both packages for various reasons, is there any way around this error?