diff --git a/gtsam_unstable/discrete/tests/testLoopyBelief.cpp b/gtsam_unstable/discrete/tests/testLoopyBelief.cpp
index 6561949b14..eac0d834e6 100644
--- a/gtsam_unstable/discrete/tests/testLoopyBelief.cpp
+++ b/gtsam_unstable/discrete/tests/testLoopyBelief.cpp
@@ -8,6 +8,7 @@
 #include <CppUnitLite/TestHarness.h>
 #include <gtsam/discrete/DecisionTreeFactor.h>
 #include <gtsam/discrete/DiscreteFactorGraph.h>
+#include <gtsam/discrete/DiscreteConditional.h>
 #include <gtsam/inference/VariableIndex.h>
 
 #include <boost/assign/list_of.hpp>