diff --git a/src/util-inl.h b/src/util-inl.h
index 99d470205e1ce7..1abebf6e1374e8 100644
--- a/src/util-inl.h
+++ b/src/util-inl.h
@@ -27,6 +27,18 @@
 #include <cstring>
 #include "util.h"
 
+// These are defined by <sys/byteorder.h> or <netinet/in.h> on some systems.
+// To avoid warnings, undefine them before redefining them.
+#ifdef BSWAP_2
+# undef BSWAP_2
+#endif
+#ifdef BSWAP_4
+# undef BSWAP_4
+#endif
+#ifdef BSWAP_8
+# undef BSWAP_8
+#endif
+
 #if defined(_MSC_VER)
 #include <intrin.h>
 #define BSWAP_2(x) _byteswap_ushort(x)