diff --git a/python-schedutils/schedutils.c b/python-schedutils/schedutils.c
index 65f1da7..d852d5d 100644
--- a/python-schedutils/schedutils.c
+++ b/python-schedutils/schedutils.c
@@ -179,7 +179,7 @@
 		CPU_SET_S(cpu, cpusetsize, cpus);
 	}
 
-	i = sched_setaffinity(pid, sizeof(cpus), cpus);
+	i = sched_setaffinity(pid, cpusetsize, cpus);
 	CPU_FREE(cpus);
 
 	if (i < 0)