diff --git a/include/boost/config/platform/bsd.hpp b/include/boost/config/platform/bsd.hpp
index 101adfd1..0af5364f 100644
--- a/include/boost/config/platform/bsd.hpp
+++ b/include/boost/config/platform/bsd.hpp
@@ -28,6 +28,14 @@
 #  define BOOST_HAS_NL_TYPES_H
 #endif
 
+//
+// FreeBSD 3.x has pthreads support, but defines _POSIX_THREADS in <pthread.h>
+// and not in <unistd.h>
+//
+#if defined(__FreeBSD__) && (__FreeBSD__ <= 3)
+#  define BOOST_HAS_PTHREADS
+#endif
+
 //
 // No wide character support in the BSD header files:
 //