stableUnfoldingVars :: Unfolding -> VarSet
stableUnfoldingVars (CoreUnfolding { uf_tmpl = rhs, uf_src = src })
| isStableSource src = exprFreeVars rhs
-stableUnfoldingVars (DFunUnfolding _ _ args) = exprsFreeVars args
+stableUnfoldingVars (DFunUnfolding _ _ args) = exprsFreeVars (dfunArgExprs args)
stableUnfoldingVars _ = emptyVarSet
\end{code}