diff --git a/src/types.h b/src/types.h
index 0c024ae..5238661 100644
--- a/src/types.h
+++ b/src/types.h
@@ -69,7 +69,9 @@ static FORCEINLINE uint UintMax(uint a, uint b) { return a > b ? a : b; }
 #define DWORD(x) (*(uint32*)&(x))
 #define XY(x, y) ((y)*64+(x))
 
+#ifndef swap16
 static inline uint16 swap16(uint16 v) { return (v << 8) | (v >> 8); }
+#endif
 
 void NORETURN Die(const char *error);
 void Warning(const char *error);