diff --git a/setup.py b/setup.py
index 36a0d77..5c37e45 100644
--- a/setup.py
+++ b/setup.py
@@ -1261,7 +1261,7 @@
                 )
             libraries = []
 
-        elif platform in ('freebsd5', 'freebsd6', 'freebsd7', 'freebsd8'):
+        elif platform in ('freebsd4', 'freebsd5', 'freebsd6', 'freebsd7', 'freebsd8'):
             # FreeBSD's P1003.1b semaphore support is very experimental
             # and has many known problems. (as of June 2008)
             macros = dict(                  # FreeBSD