diff --git a/src/core/features.h b/src/core/features.h
index 0348fc04..46caff58 100644
--- a/src/core/features.h
+++ b/src/core/features.h
@@ -26,7 +26,7 @@
 #define JANET_FEATURES_H_defined
 
 #if defined(__NetBSD__) || defined(__APPLE__) || defined(__OpenBSD__) \
-    || defined(__bsdi__) || defined(__DragonFly__)
+    || defined(__bsdi__) || defined(__DragonFly__) || defined(__FreeBSD__)
 /* Use BSD source on any BSD systems, include OSX */
 # define _BSD_SOURCE
 # define _POSIX_C_SOURCE 200809L
@@ -67,7 +67,7 @@
 #endif
 
 /* Needed for several things when building with -std=c99. */
-#if !__BSD_VISIBLE && defined(__DragonFly__)
+#if !__BSD_VISIBLE && (defined(__DragonFly__) || defined(__FreeBSD__))
 #define __BSD_VISIBLE 1
 #endif