diff --git a/meta-facebook/meta-bletchley/conf/machine/bletchley.conf b/meta-facebook/meta-bletchley/conf/machine/bletchley.conf
index c0df356..1d1a5b8 100644
--- a/meta-facebook/meta-bletchley/conf/machine/bletchley.conf
+++ b/meta-facebook/meta-bletchley/conf/machine/bletchley.conf
@@ -16,4 +16,5 @@
 PREFERRED_PROVIDER_virtual/phosphor-led-manager-config-native = "bletchley-led-manager-config-native"
 
 OBMC_HOST_INSTANCES = "1 2 3 4 5 6"
-
+# Primary chassis as Sled plus secondary chassis in N slots.
+OBMC_CHASSIS_INSTANCES = "0 ${OBMC_HOST_INSTANCES}"