-/* glibc defines (_IO_)putc_unlocked() to __overflow() in some cases. */
-#ifdef HAVE_STRUCT__IO_FILE__FILENO
-HOOK_FD2(int, __overflow, f->_fileno, _IO_FILE *, f, int, ch)
+/* glibc defines (_IO_)putc_unlocked() to a macro which either updates the
+ * output buffer or calls __overflow(). As this code is inlined we can't
+ * handle the first case, but if __overflow() is called we can color that
+ * part. As writes to stderr are never buffered, __overflow() is always called
+ * and everything works fine. This is only a problem if stdout is dupped to
+ * stderr (which shouldn't be the case too often). */
+#if defined(HAVE_STRUCT__IO_FILE__FILENO) && defined(HAVE___OVERFLOW)
+/* _IO_FILE is glibc's representation of FILE. */
+HOOK_FILE2(int, __overflow, f, _IO_FILE *, f, int, ch)
+#endif
+/* Same for FreeBSD's libc. However it's more aggressive: The inline writing
+ * and __swbuf() are also used for normal output (e.g. putc()). Writing to
+ * stderr is still fine; it always calls __swbuf() as stderr is always
+ * unbufferd. */
+#ifdef HAVE___SWBUF
+HOOK_FILE2(int, __swbuf, f, int, c, FILE *, f)