diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
index 6854be6df..492f41bc2 100644
--- a/RELEASE_NOTES.md
+++ b/RELEASE_NOTES.md
@@ -10,6 +10,7 @@ What's New
 
 ### NEXT VERSION:
 * (patch) #630 - Make DefaultMessageFactory reflect only over QF/n assemblies (gbirchmeier)
+* (patch) #643 - add 1156 (ApplExtId) to FIXT11.xml (gbirchmeier)
 
 ### v1.10.0:
 * (patch) #505 - Fix ObjectDisposedException when SocketInitiator is stopped before connection attempt fails (musashibg)
diff --git a/spec/fix/FIXT11.xml b/spec/fix/FIXT11.xml
index 15054a8a2..409d91fb0 100644
--- a/spec/fix/FIXT11.xml
+++ b/spec/fix/FIXT11.xml
@@ -30,6 +30,7 @@
     <component name='HopGrp' required='N'/>
     <field name='ApplVerID' required='N'/>
     <field name='CstmApplVerID' required='N'/>
+    <field name='ApplExtID' required='N' />
   </header>
   <trailer>
     <field name='SignatureLength' required='N'/>
@@ -309,5 +310,6 @@
     <field name='RefApplVerID' number='1130' type='STRING'/>
     <field name='RefCstmApplVerID' number='1131' type='STRING'/>
     <field name='DefaultApplVerID' number='1137' type='STRING'/>
+    <field name='ApplExtID' number='1137' type='INT'/>
   </fields>
 </fix>