diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index 7a181d4..23c1f00 100644
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -120,7 +120,7 @@ typedef SSIZE_T	ssize_t;
 #include <resolv.h>	/* defines BYTE_ORDER on HPUX and Solaris */
 #endif
 
-#if defined(__APPLE__) || defined (BSD)
+#if defined(__APPLE__) || defined (BSD) || defined(__FreeBSD_kernel__)
 # define MDB_USE_POSIX_SEM	1
 # define MDB_FDATASYNC		fsync
 #elif defined(ANDROID)