diff --git a/configure.ac b/configure.ac
index 6d35450b0..bd618e577 100644
--- a/configure.ac
+++ b/configure.ac
@@ -712,6 +712,10 @@ case "${host}" in
         # keeps things simple
         require_iconv=no
         ;;
+    *-apple-darwin*)
+        AC_DEFINE(_DARWIN_C_SOURCE, 900000L,
+                  Expose all libc features (__DARWIN_C_FULL).)
+        ;;
     *)
        ;;
 esac