diff --git a/libnetutil/netutil.cc b/libnetutil/netutil.cc
index ca7562539..5c265842b 100644
--- a/libnetutil/netutil.cc
+++ b/libnetutil/netutil.cc
@@ -937,7 +937,7 @@ int pcap_select(pcap_t *p, struct timeval *timeout) {
     return -1;
 
   FD_ZERO(&rfds);
-  FD_SET(fd, &rfds);
+  checked_fd_set(fd, &rfds);
 
   do {
     errno = 0;
diff --git a/tcpip.cc b/tcpip.cc
index ed502fe1c..ff542d935 100644
--- a/tcpip.cc
+++ b/tcpip.cc
@@ -1758,7 +1758,7 @@ int recvtime(int sd, char *buf, int len, int seconds, int *timedout) {
   timeout.tv_sec = seconds;
   timeout.tv_usec = 0;
   FD_ZERO(&readfd);
-  FD_SET(sd, &readfd);
+  checked_fd_set(sd, &readfd);
   if (timedout)
     *timedout = 0;
   res = select(sd + 1, &readfd, NULL, NULL, &timeout);