diff --git a/include/haproxy/compat.h b/include/haproxy/compat.h
index ad91b901c..39f7af7a6 100644
--- a/include/haproxy/compat.h
+++ b/include/haproxy/compat.h
@@ -120,6 +120,11 @@ typedef struct { } empty_t;
 })
 #endif
 
+/* always set a _POSIX_VERSION if there isn't any, in order to ease compares */
+#ifndef _POSIX_VERSION
+# define _POSIX_VERSION 0
+#endif
+
 /* this is for libc5 for example */
 #ifndef TCP_NODELAY
 #define TCP_NODELAY     1