diff --git a/src/core/util.h b/src/core/util.h
index a77c95fe..1ab5d4e7 100644
--- a/src/core/util.h
+++ b/src/core/util.h
@@ -31,10 +31,14 @@
 #endif
 
 /* For internal usage */
-#ifndef _POSIX_C_SOURCE
+#if !defined(_POSIX_C_SOURCE)
 #define _POSIX_C_SOURCE 200112L
 #endif
 
+#if !defined(_BSD_SOURCE) && defined(JANET_BSD)
+#define _BSD_SOURCE 1
+#endif
+
 /* Handle runtime errors */
 #ifndef janet_exit
 #include <stdio.h>
diff --git a/src/include/janet.h b/src/include/janet.h
index 59cefebf..664b803f 100644
--- a/src/include/janet.h
+++ b/src/include/janet.h
@@ -49,7 +49,6 @@ extern "C" {
 #if defined(__FreeBSD__) || defined(__DragonFly__) || \
     defined(__NetBSD__) || defined(__OpenBSD__)
 #define JANET_BSD 1
-#define _BSD_SOURCE 1
 #endif
 
 /* Check for Mac */