diff --git a/gtsam/hybrid/HybridGaussianFactorGraph.h b/gtsam/hybrid/HybridGaussianFactorGraph.h
index c2e50ace8..e3c1e2d55 100644
--- a/gtsam/hybrid/HybridGaussianFactorGraph.h
+++ b/gtsam/hybrid/HybridGaussianFactorGraph.h
@@ -18,6 +18,7 @@
 
 #pragma once
 
+#include <gtsam/discrete/DiscreteFactorGraph.h>
 #include <gtsam/discrete/DiscreteKey.h>
 #include <gtsam/hybrid/HybridFactor.h>
 #include <gtsam/hybrid/HybridFactorGraph.h>