diff --git a/simgear/scene/model/ConditionNode.cxx b/simgear/scene/model/ConditionNode.cxx
index 8003caa1..56460bef 100644
--- a/simgear/scene/model/ConditionNode.cxx
+++ b/simgear/scene/model/ConditionNode.cxx
@@ -15,6 +15,10 @@
 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 //
 
+#ifdef HAVE_CONFIG_H
+#  include <simgear_config.h>
+#endif
+
 #include "ConditionNode.hxx"
 
 #include <simgear/math/SGMath.hxx>