diff --git a/include/rdma/ib_cm.h b/include/rdma/ib_cm.h
index c8f94e8..83f77ac 100644
--- a/include/rdma/ib_cm.h
+++ b/include/rdma/ib_cm.h
@@ -38,6 +38,9 @@
 #include <rdma/ib_mad.h>
 #include <rdma/ib_sa.h>
 
+/* ib_cm and ib_user_cm modules share /sys/class/infiniband_cm */
+extern struct class cm_class;
+
 enum ib_cm_state {
 	IB_CM_IDLE,
 	IB_CM_LISTEN,