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diff --git a/system/doc/design_principles/appup_cookbook.xml b/system/doc/design_principles/appup_cookbook.xml
index eebe6ba7b4..798b23d847 100644
--- a/system/doc/design_principles/appup_cookbook.xml
+++ b/system/doc/design_principles/appup_cookbook.xml
@@ -640,5 +640,23 @@ code_change(_OldVsn, State, port) ->
updates etc. can be used without having to specify <c>.appup</c>
files.</p>
</section>
+
+ <section>
+ <title>Emulator Upgrade from pre OTP R15</title>
+ <p>From OTP R15, an emulator upgrade is performed by restarting
+ the emulator with new versions of the core applications
+ (<c>kernel</c>, <c>stdlib</c> and <c>sasl</c>) before loading code
+ and running upgrade instruction for other applications. For this
+ to work, the release to upgrade from must includes OTP R15 or
+ later. For the case where the release to upgrade from includes an
+ earlier emulator version, <c>systools:make_relup</c> will create a
+ backwards compatible relup file. This means that all upgrade
+ instructions will be executed before the emulator is
+ restarted. The new application code will therefore be loaded into
+ the old emulator. If the new code is compiled with the new
+ emulator, there might be cases where the beam format has changed
+ and beam files can not be loaded. To overcome this problem, the
+ new code should be compiled with the old emulator.</p>
+ </section>
</chapter>