--- a/rail.h
+++ b/rail.h
@@ -153,21 +153,21 @@
  * Maps a trackdir to the bit that stores its status in the map arrays, in the
  * direction along with the trackdir.
  */
-const byte _signal_along_trackdir[TRACKDIR_END];
+extern const byte _signal_along_trackdir[TRACKDIR_END];
 static inline byte SignalAlongTrackdir(Trackdir trackdir) {return _signal_along_trackdir[trackdir];}
 
 /**
  * Maps a trackdir to the bit that stores its status in the map arrays, in the
  * direction against the trackdir.
  */
-const byte _signal_against_trackdir[TRACKDIR_END];
+extern const byte _signal_against_trackdir[TRACKDIR_END];
 static inline byte SignalAgainstTrackdir(Trackdir trackdir) { return _signal_against_trackdir[trackdir]; }
 
 /**
  * Maps a Track to the bits that store the status of the two signals that can
  * be present on the given track.
  */
-const byte _signal_on_track[TRACK_END];
+extern const byte _signal_on_track[TRACK_END];
 static inline byte SignalOnTrack(Track track) { return _signal_on_track[track]; }
 
 /*
@@ -247,7 +247,7 @@
 /**
  * Maps a trackdir to the reverse trackdir.
  */
-const Trackdir _reverse_trackdir[TRACKDIR_END];
+extern const Trackdir _reverse_trackdir[TRACKDIR_END];
 static inline Trackdir ReverseTrackdir(Trackdir trackdir) { return _reverse_trackdir[trackdir]; }
 
 /**
@@ -280,48 +280,48 @@
  * ahead. This will be the same trackdir for diagonal trackdirs, but a
  * different (alternating) one for straight trackdirs
  */
-const Trackdir _next_trackdir[TRACKDIR_END];
+extern const Trackdir _next_trackdir[TRACKDIR_END];
 static inline Trackdir NextTrackdir(Trackdir trackdir) { return _next_trackdir[trackdir]; }
 
 /**
  * Maps a track to all tracks that make 90 deg turns with it.
  */
-const TrackBits _track_crosses_tracks[TRACK_END];
+extern const TrackBits _track_crosses_tracks[TRACK_END];
 static inline TrackBits TrackCrossesTracks(Track track) { return _track_crosses_tracks[track]; }
 
 /**
  * Maps a trackdir to the (4-way) direction the tile is exited when following
  * that trackdir.
  */
-const DiagDirection _trackdir_to_exitdir[TRACKDIR_END];
+extern const DiagDirection _trackdir_to_exitdir[TRACKDIR_END];
 static inline DiagDirection TrackdirToExitdir(Trackdir trackdir) { return _trackdir_to_exitdir[trackdir]; }
 
 /**
  * Maps a track and an (4-way) dir to the trackdir that represents the track
  * with the exit in the given direction.
  */
-const Trackdir _track_exitdir_to_trackdir[TRACK_END][DIAGDIR_END];
+extern const Trackdir _track_exitdir_to_trackdir[TRACK_END][DIAGDIR_END];
 static inline Trackdir TrackExitdirToTrackdir(Track track, DiagDirection diagdir) { return _track_exitdir_to_trackdir[track][diagdir]; }
 
 /**
  * Maps a track and a full (8-way) direction to the trackdir that represents
  * the track running in the given direction.
  */
-const Trackdir _track_direction_to_trackdir[TRACK_END][DIR_END];
+extern const Trackdir _track_direction_to_trackdir[TRACK_END][DIR_END];
 static inline Trackdir TrackDirectionToTrackdir(Track track, Direction dir) { return _track_direction_to_trackdir[track][dir]; }
 
 /**
  * Maps a (4-way) direction to the diagonal trackdir that runs in that
  * direction.
  */
-const Trackdir _dir_to_diag_trackdir[DIAGDIR_END];
+extern const Trackdir _dir_to_diag_trackdir[DIAGDIR_END];
 static inline Trackdir DiagdirToDiagTrackdir(DiagDirection diagdir) { return _dir_to_diag_trackdir[diagdir]; }
 
 /**
  * Maps a trackdir to the trackdirs that can be reached from it (ie, when
  * entering the next tile. This
  */
-const TrackdirBits _exitdir_reaches_trackdirs[DIAGDIR_END];
+extern const TrackdirBits _exitdir_reaches_trackdirs[DIAGDIR_END];
 /* Note that there is no direct table for this function (there used to be),
  * but it uses two simpeler tables to achieve the result */
 static inline TrackdirBits TrackdirReachesTrackdirs(Trackdir trackdir) { return _exitdir_reaches_trackdirs[TrackdirToExitdir(trackdir)]; }
@@ -329,13 +329,13 @@
 /**
  * Maps a trackdir to all trackdirs that make 90 deg turns with it.
  */
-const TrackdirBits _track_crosses_trackdirs[TRACKDIR_END];
+extern const TrackdirBits _track_crosses_trackdirs[TRACKDIR_END];
 static inline TrackdirBits TrackdirCrossesTrackdirs(Trackdir trackdir) { return _track_crosses_trackdirs[TrackdirToTrack(trackdir)]; }
 
 /**
  * Maps a (4-way) direction to the reverse.
  */
-const DiagDirection _reverse_diagdir[DIAGDIR_END];
+extern const DiagDirection _reverse_diagdir[DIAGDIR_END];
 static inline DiagDirection ReverseDiagdir(DiagDirection diagdir) { return _reverse_diagdir[diagdir]; }
 
 /* Checks if a given Track is diagonal */