diff --git a/libgrive/src/util/OS.hh b/libgrive/src/util/OS.hh
index bd28e30..a5f3c98 100644
--- a/libgrive/src/util/OS.hh
+++ b/libgrive/src/util/OS.hh
@@ -24,6 +24,10 @@
 
 #include <string>
 
+#if defined(__FreeBSD__)
+#define off64_t off_t
+#endif
+
 namespace gr {
 
 class DateTime ;