diff --git a/include/haproxy/compat.h b/include/haproxy/compat.h
index 886b7a365..84cdbe0d5 100644
--- a/include/haproxy/compat.h
+++ b/include/haproxy/compat.h
@@ -85,6 +85,16 @@ typedef struct { } empty_t;
 #define BITS_PER_INT    (8*sizeof(int))
 #endif
 
+#ifndef __WORDSIZE
+# if defined(__SIZEOF_LONG__) && __SIZEOF_LONG__ == 4
+#  define __WORDSIZE 32
+# elif defined(__SIZEOF_LONG__) && __SIZEOF_LONG__ == 8
+#  define __WORDSIZE 64
+# else
+#  error "Unknown machine word size (__WORDSIZE, __SIZEOF_LONG)"
+# endif
+#endif
+
 #ifndef MIN
 #define MIN(a, b) (((a) < (b)) ? (a) : (b))
 #endif