  Let $G$ be a real quaternionic classical group $\GL_n(\bH)$, $\Sp(p,q)$ or
$\oO^*(2n)$. We define an extension $\breve G$ of $G$ with the following
property: it contains $G$ as a subgroup of index two, and for every $x\in G$,
there is an element $\breve g\in \breve G\setminus G$ such that $\breve g
x\breve{g}^{-1}=x^{-1}$. This is similar to Moeglin-Vigneras-Waldspurger's
extensions of non-quaternionic classical groups.
