diff --git a/src/FDM/JSBSim/input_output/FGPropertyManager.h b/src/FDM/JSBSim/input_output/FGPropertyManager.h
index fdd5c4077..8f191fe87 100644
--- a/src/FDM/JSBSim/input_output/FGPropertyManager.h
+++ b/src/FDM/JSBSim/input_output/FGPropertyManager.h
@@ -35,9 +35,14 @@ SENTRY
 INCLUDES
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
 
+#ifdef HAVE_CONFIG_H
+#  include <config.h>
+#endif
+
 #include <string>
 #include <iostream>
-#include "simgear/props/props.hxx"
+#include <simgear/props/props.hxx>
+#include <simgear/math/SGMath.hxx>
 
 #include "FGJSBBase.h"