diff --git a/src/system/libroot/posix/spawn.cpp b/src/system/libroot/posix/spawn.cpp
index 655f42e37b..3f362c89ff 100644
--- a/src/system/libroot/posix/spawn.cpp
+++ b/src/system/libroot/posix/spawn.cpp
@@ -299,7 +299,8 @@ posix_spawnattr_setflags(posix_spawnattr_t *_attr, short flags)
 		return EINVAL;
 
 	if ((flags & ~(POSIX_SPAWN_RESETIDS | POSIX_SPAWN_SETPGROUP
-			| POSIX_SPAWN_SETSIGDEF | POSIX_SPAWN_SETSIGMASK)) != 0) {
+			| POSIX_SPAWN_SETSIGDEF | POSIX_SPAWN_SETSIGMASK
+			| POSIX_SPAWN_SETSID)) != 0) {
 		return EINVAL;
 	}