diff --git a/gtsam/hybrid/HybridConditional.cpp b/gtsam/hybrid/HybridConditional.cpp
index 463f3e283..f57237e93 100644
--- a/gtsam/hybrid/HybridConditional.cpp
+++ b/gtsam/hybrid/HybridConditional.cpp
@@ -22,7 +22,7 @@
 #include <gtsam/inference/Conditional-inst.h>
 #include <gtsam/inference/Key.h>
 
-#include <iostream>
+#include <string>
 
 namespace gtsam {