  The existence of isospin admixtures in the physical $\Lambda$, $\pi^o$
complicates the extraction of Delta I=3/2 non-leptonic hyperon decay amplitudes
from experimental data, allowing contributions associated with large Delta
I=1/2 amplitudes to appear in the (nominally) Delta I=3/2 amplitudes obtained
ignoring these admixtures. We show how to correct for this effect to leading
order in $(m_d-m_u)$ and extract the true Delta I=3/2 amplitudes. The resulting
corrections are modest ($<25\%$) for s-waves, but extremely large, $\simeq
100\%$ and $\simeq 400\%$ for $\Lambda$ and $\Xi$ p-waves, respectively.
