diff --git a/racket/src/racket/gc2/sighand.c b/racket/src/racket/gc2/sighand.c
index f93f5a066d..dff2fd510f 100644
--- a/racket/src/racket/gc2/sighand.c
+++ b/racket/src/racket/gc2/sighand.c
@@ -227,7 +227,7 @@ static void initialize_signal_handler(GCTYPE *gc)
 # ifdef NEED_SIGACTION
   {
     struct sigaction act, oact;
-    memset(&act, 0, sizeof(sigaction));
+    memset(&act, 0, sizeof(act));
     act.sa_sigaction = fault_handler;
     sigemptyset(&act.sa_mask);
     /* In Racket, SIGCHLD or SIGINT handling may trigger a write barrier: */
@@ -269,7 +269,7 @@ static void remove_signal_handler(GCTYPE *gc)
 # ifdef NEED_SIGACTION
   {
     struct sigaction act, oact;
-    memset(&act, 0, sizeof(sigaction));
+    memset(&act, 0, sizeof(act));
     act.sa_handler = SIG_DFL;
     sigemptyset(&act.sa_mask);
     act.sa_flags = SA_SIGINFO;