diff --git a/src/FDM/LaRCsim.cxx b/src/FDM/LaRCsim.cxx
index 43223bf4c..96aed0b44 100644
--- a/src/FDM/LaRCsim.cxx
+++ b/src/FDM/LaRCsim.cxx
@@ -34,6 +34,7 @@
 #include <FDM/LaRCsim/ls_interface.h>
 #include <FDM/LaRCsimIC.hxx>
 #include <FDM/UIUCModel/uiuc_aircraft.h>
+#include <Model/acmodel.hxx>
 
 #include "IO360.hxx"
 #include "LaRCsim.hxx"
diff --git a/src/FDM/YASim/YASim.cxx b/src/FDM/YASim/YASim.cxx
index c5352f6b9..c7b283893 100644
--- a/src/FDM/YASim/YASim.cxx
+++ b/src/FDM/YASim/YASim.cxx
@@ -3,6 +3,7 @@
 #include <simgear/xml/easyxml.hxx>
 #include <Main/globals.hxx>
 #include <Main/fg_props.hxx>
+#include <Model/acmodel.hxx>
 
 #include "FGFDM.hpp"
 #include "Atmosphere.hpp"
diff --git a/src/FDM/flight.cxx b/src/FDM/flight.cxx
index 3ce32a6c8..362fc062b 100644
--- a/src/FDM/flight.cxx
+++ b/src/FDM/flight.cxx
@@ -34,6 +34,7 @@
 #include <FDM/LaRCsim/ls_interface.h>
 #include <Main/globals.hxx>
 #include <Main/fg_props.hxx>
+#include <Model/acmodel.hxx>
 
 #include "flight.hxx"
 
diff --git a/src/FDM/flight.hxx b/src/FDM/flight.hxx
index 8dc1aaebb..7f61f2149 100644
--- a/src/FDM/flight.hxx
+++ b/src/FDM/flight.hxx
@@ -93,7 +93,6 @@
 // #include <simgear/timing/timestamp.hxx>
 
 #include <Main/fgfs.hxx>
-#include <Model/acmodel.hxx>
 #include <Model/model.hxx>
 #include <Main/location.hxx>
 
@@ -101,6 +100,8 @@ SG_USING_STD(list);
 SG_USING_STD(vector);
 SG_USING_STD(string);
 
+class FGAircraftModel;
+
 
 typedef double FG_VECTOR_3[3];