diff --git a/src/header/unistd/cbindgen.toml b/src/header/unistd/cbindgen.toml
index 2c03074df9c2f42ddbf8eb750694249ddcf6002d..585796ed3467e10dadcdd67ad7b8a56bbfdb1811 100644
--- a/src/header/unistd/cbindgen.toml
+++ b/src/header/unistd/cbindgen.toml
@@ -6,3 +6,7 @@ style = "Tag"
 
 [enum]
 prefix_with_name = true
+
+[defines]
+"target_os = linux" = "__linux__"
+"target_os = redox" = "__redox__"