diff --git a/prebuild.xml b/prebuild.xml
index e408ccd26f..48bb2d3f48 100644
--- a/prebuild.xml
+++ b/prebuild.xml
@@ -3005,6 +3005,7 @@
       <Reference name="OpenSim.Framework.Statistics"/>
       <Reference name="OpenSim.Region.Framework"/>
       <Reference name="OpenSim.Region.CoreModules"/>
+      <Reference name="OpenSim.Region.OptionalModules"/>
       <Reference name="OpenSim.Region.Physics.Manager"/>
       <Reference name="OpenSim.Services.Interfaces"/>