diff --git a/src/lisp/interrupt.c b/src/lisp/interrupt.c
index b6332f59ba65c373a9da9957f48ab518114ba66e..25fb2f651462a44f5b3c0473605b9b132cd10690 100644
--- a/src/lisp/interrupt.c
+++ b/src/lisp/interrupt.c
@@ -175,7 +175,7 @@ copy_sigmask(sigset_t *dst, sigset_t *src)
 #ifndef __linux__
     *dst = *src;
 #else
-    memcpy(dst, src, NSIG / 8);
+    memcpy(dst, src, NSIG / CHAR_BIT);
 #endif
 }