diff --git a/newgrf_station.c b/newgrf_station.c
index cb02b9b2ff..2b699e2171 100644
--- a/newgrf_station.c
+++ b/newgrf_station.c
@@ -137,6 +137,9 @@ void SetCustomStationSpec(StationSpec *statspec)
 	StationClass *station_class;
 	int i;
 
+	/* If the station has already been allocated, don't reallocate it. */
+	if (statspec->allocated) return;
+
 	assert(statspec->sclass < STAT_CLASS_MAX);
 	station_class = &station_classes[statspec->sclass];
 
@@ -144,6 +147,7 @@ void SetCustomStationSpec(StationSpec *statspec)
 	station_class->spec = realloc(station_class->spec, station_class->stations * sizeof(*station_class->spec));
 
 	station_class->spec[i] = statspec;
+	statspec->allocated = true;
 }
 
 /**
diff --git a/newgrf_station.h b/newgrf_station.h
index 8e01c4923c..b7ec6063e8 100644
--- a/newgrf_station.h
+++ b/newgrf_station.h
@@ -21,6 +21,8 @@ typedef struct StationSpec {
 	uint32 grfid; ///< ID of GRF file station belongs to.
 	int localidx; ///< Index within GRF file of station.
 
+	bool allocated; ///< Flag whether this station has been added to a station class list
+
 	StationClassID sclass; ///< The class to which this spec belongs.
 	StringID name; ///< Name of this station.