<sect2 id="instance-decls">
<title>Instance declarations</title>
-<sect3>
+<sect3 id="instance-overlap">
<title>Overlapping instances</title>
<para>
In general, <emphasis>GHC requires that that it be unambiguous which instance
GHC will instead pick (C), without complaining about
the problem of subsequent instantiations.
</para>
+<para>
+Because overlaps are checked and reported lazily, as described above, you need
+the <option>-fallow-overlapping-instances</option> in the module that <emphasis>calls</emphasis>
+the overloaded function, rather than in the module that <emphasis>defines</emphasis> it.</para>
+
</sect3>
<sect3>