diff --git a/VirtualRobot/Nodes/RobotNodeHemisphere.cpp b/VirtualRobot/Nodes/RobotNodeHemisphere.cpp
index 9eec7020545830697654449ad69f85ab8f7f9842..9a3ad650e568c7129a8367eed3e6a20705a5dd9c 100644
--- a/VirtualRobot/Nodes/RobotNodeHemisphere.cpp
+++ b/VirtualRobot/Nodes/RobotNodeHemisphere.cpp
@@ -128,7 +128,7 @@ namespace VirtualRobot
             SceneObjectPtr parent,
             const std::vector<SceneObjectPtr>& children)
     {
-        VR_ASSERT_MESSAGE(first xor sub, first.has_value() << " / " sub.has_value());
+        VR_ASSERT_MESSAGE(first xor sub, first.has_value() << " / " << sub.has_value());
 
         // The second node needs to store a reference to the first node.
         if (second)