diff --git a/lib/std/c.zig b/lib/std/c.zig
index aeb48a3cc27c9403e7794e2d8ca2b31ff95ed22a..ac4b3cd1d0a4c922633716df9cf5be4859277ea8 100644
--- a/lib/std/c.zig
+++ b/lib/std/c.zig
@@ -1914,7 +1914,7 @@ pub const LC = enum(c_int) {
     IDENTIFICATION = 12,
 };
 
-pub extern "c" fn setlocale(category: LC, locale: ?[*:0]const u8) [*:0]const u8;
+pub extern "c" fn setlocale(category: LC, locale: ?[*:0]const u8) ?[*:0]const u8;
 
 pub const getcontext = if (builtin.target.isAndroid())
     @compileError("android bionic libc does not implement getcontext")