diff --git a/src/FDM/ExternalNet/ExternalNet.hxx b/src/FDM/ExternalNet/ExternalNet.hxx
index cbefc1ed0..41e848d9f 100644
--- a/src/FDM/ExternalNet/ExternalNet.hxx
+++ b/src/FDM/ExternalNet/ExternalNet.hxx
@@ -30,6 +30,7 @@
 
 #include <Network/net_ctrls.hxx>
 #include <Network/net_fdm.hxx>
+#include <FDM/flight.hxx>
 
 
 class HTTPClient : public netBufferChannel
diff --git a/src/FDM/ExternalPipe/ExternalPipe.hxx b/src/FDM/ExternalPipe/ExternalPipe.hxx
index 56bcccdbc..825066948 100644
--- a/src/FDM/ExternalPipe/ExternalPipe.hxx
+++ b/src/FDM/ExternalPipe/ExternalPipe.hxx
@@ -29,6 +29,7 @@
 
 #include <Network/net_ctrls.hxx>
 #include <Network/net_fdm.hxx>
+#include <FDM/flight.hxx>
 
 
 class FGExternalPipe: public FGInterface {