diff --git a/macros.h b/macros.h
--- a/macros.h
+++ b/macros.h
@@ -160,6 +160,7 @@ static inline int64 myabs64(int64 a) { i
 static inline void swap_byte(byte *a, byte *b) { byte t = *a; *a = *b; *b = t; }
 static inline void swap_uint16(uint16 *a, uint16 *b) { uint16 t = *a; *a = *b; *b = t; }
 static inline void swap_int16(int16 *a, int16 *b) { int16 t = *a; *a = *b; *b = t; }
+static inline void swap_int32(int32 *a, int32 *b) { int32 t = *a; *a = *b; *b = t; }
 static inline void swap_tile(TileIndex *a, TileIndex *b) { TileIndex t = *a; *a = *b; *b = t; }