diff --git a/libc/include/bits/waitpid.h b/libc/include/bits/waitpid.h
index 2ed3b15e..dbe37ed2 100644
--- a/libc/include/bits/waitpid.h
+++ b/libc/include/bits/waitpid.h
@@ -6,5 +6,6 @@
 #define _SIGBIT 0x100
 
 #define WNOHANG 1
+#define WUNTRACED 2 // Unused.
 
 #endif