diff --git a/error.c b/error.c
index 07fa04627e..113264eeb7 100644
--- a/error.c
+++ b/error.c
@@ -2437,9 +2437,6 @@ get_syserr(int n)
 static VALUE
 syserr_initialize(int argc, VALUE *argv, VALUE self)
 {
-#if !defined(_WIN32)
-    char *strerror();
-#endif
     const char *err;
     VALUE mesg, error, func, errmsg;
     VALUE klass = rb_obj_class(self);