diff --git a/src/thread/pthread_cancel.c b/src/thread/pthread_cancel.c
index 1b71aa423399220f70a0a35066af8b04d8d0339a..a507f9237a9d55852167ad1733f27f39015374d2 100644
--- a/src/thread/pthread_cancel.c
+++ b/src/thread/pthread_cancel.c
@@ -1,3 +1,4 @@
+#include <string.h>
 #include "pthread_impl.h"
 #include "syscall.h"
 #include "libc.h"
@@ -80,7 +81,7 @@ static void init_cancellation()
 		.sa_flags = SA_SIGINFO | SA_RESTART,
 		.sa_sigaction = cancel_handler
 	};
-	sigfillset(&sa.sa_mask);
+	memset(&sa.sa_mask, -1, _NSIG/8);
 	__libc_sigaction(SIGCANCEL, &sa, 0);
 }