- compatibility (e.g., for LSB 2.0.1). */
-#if defined __GETOPT_PREFIX && !defined __need_getopt
-# define __getopt_argv_const /* empty */
-#else
-# define __getopt_argv_const const
+ compatibility (e.g., for LSB 2.0.1).
+
+ This used to be `#if defined __GETOPT_PREFIX && !defined __need_getopt',
+ but it caused redefinition warnings if both unistd.h and getopt.h were
+ included, since unistd.h includes getopt.h having previously defined
+ __need_getopt.
+
+ The only place where __getopt_argv_const is used is in definitions
+ of getopt_long and getopt_long_only below, but these are visible
+ only if __need_getopt is not defined, so it is quite safe to rewrite
+ the conditional as follows:
+*/
+#if !defined __need_getopt
+# if defined __GETOPT_PREFIX
+# define __getopt_argv_const /* empty */
+# else
+# define __getopt_argv_const const
+# endif