diff --git a/ndhc/dhcp.c b/ndhc/dhcp.c
index 44df7cb..7421ff7 100644
--- a/ndhc/dhcp.c
+++ b/ndhc/dhcp.c
@@ -91,7 +91,7 @@ static ssize_t send_dhcp_cooked(struct client_state_t *cs,
 {
     ssize_t ret = -1;
     int fd = get_udp_unicast_socket();
-    if (fd == -1)
+    if (fd < 0)
         goto out;
 
     struct sockaddr_in raddr = {
@@ -99,7 +99,7 @@ static ssize_t send_dhcp_cooked(struct client_state_t *cs,
         .sin_port = htons(DHCP_SERVER_PORT),
         .sin_addr.s_addr = cs->serverAddr,
     };
-    if (connect(fd, (struct sockaddr *)&raddr, sizeof(struct sockaddr)) == -1) {
+    if (connect(fd, (struct sockaddr *)&raddr, sizeof(struct sockaddr)) < 0) {
         log_error("%s: (%s) connect failed: %s", client_config.interface,
                   __func__, strerror(errno));
         goto out_fd;
@@ -283,7 +283,7 @@ static ssize_t send_dhcp_raw(struct dhcpmsg *payload)
 {
     ssize_t ret = -1;
     int fd = get_raw_broadcast_socket();
-    if (fd == -1)
+    if (fd < 0)
         return ret;
 
     // Send packets that are as short as possible.
diff --git a/ndhc/ifchd.c b/ndhc/ifchd.c
index 6b1a79c..647247e 100644
--- a/ndhc/ifchd.c
+++ b/ndhc/ifchd.c
@@ -92,7 +92,7 @@ static void write_resolve_conf(void)
     if (strlen(cl.namesvrs) == 0)
         return;
 
-    if (lseek(resolv_conf_fd, 0, SEEK_SET) == -1)
+    if (lseek(resolv_conf_fd, 0, SEEK_SET) < 0)
         return;
 
     char *p = cl.namesvrs;
@@ -151,14 +151,14 @@ static void write_resolve_conf(void)
     writeordie(resolv_conf_fd, "\n", 1);
 
     off = lseek(resolv_conf_fd, 0, SEEK_CUR);
-    if (off == -1) {
+    if (off < 0) {
         log_line("write_resolve_conf: lseek returned error: %s",
                 strerror(errno));
         return;
     }
   retry:
     r = ftruncate(resolv_conf_fd, off);
-    if (r == -1) {
+    if (r < 0) {
         if (errno == EINTR)
             goto retry;
         log_line("write_resolve_conf: ftruncate returned error: %s",
@@ -166,7 +166,7 @@ static void write_resolve_conf(void)
         return;
     }
     r = fsync(resolv_conf_fd);
-    if (r == -1) {
+    if (r < 0) {
         log_line("write_resolve_conf: fsync returned error: %s",
                  strerror(errno));
         return;
@@ -183,7 +183,7 @@ void perform_timezone(const char *str, size_t len)
 /* Add a dns server to the /etc/resolv.conf -- we already have a fd. */
 void perform_dns(const char *str, size_t len)
 {
-    if (!str || resolv_conf_fd == -1)
+    if (!str || resolv_conf_fd < 0)
         return;
     if (len > sizeof cl.namesvrs) {
         log_line("DNS server list is too long: %zu > %zu", len, cl.namesvrs);
@@ -210,7 +210,7 @@ void perform_hostname(const char *str, size_t len)
 {
     if (!allow_hostname || !str)
         return;
-    if (sethostname(str, len) == -1)
+    if (sethostname(str, len) < 0)
         log_line("sethostname returned %s", strerror(errno));
     else
         log_line("Set hostname: '%s'", str);
@@ -219,7 +219,7 @@ void perform_hostname(const char *str, size_t len)
 /* update "domain" and "search" in /etc/resolv.conf */
 void perform_domain(const char *str, size_t len)
 {
-    if (!str || resolv_conf_fd == -1)
+    if (!str || resolv_conf_fd < 0)
         return;
     if (len > sizeof cl.domains) {
         log_line("DNS domain list is too long: %zu > %zu", len, cl.namesvrs);
@@ -332,7 +332,7 @@ static void process_client_pipe(void)
                 client_config.interface, __func__, strerror(errno));
     }
 
-    if (execute_buffer(buf) == -1) {
+    if (execute_buffer(buf) < 0) {
         inform_execute('-');
         suicide("%s: (%s) received invalid commands: '%s'",
                 client_config.interface, __func__, buf);
@@ -343,7 +343,7 @@ static void process_client_pipe(void)
 static void do_ifch_work(void)
 {
     epollfd = epoll_create1(0);
-    if (epollfd == -1)
+    if (epollfd < 0)
         suicide("epoll_create1 failed");
 
     if (enforce_seccomp_ifch())
@@ -359,7 +359,7 @@ static void do_ifch_work(void)
 
     for (;;) {
         int r = epoll_wait(epollfd, events, 2, -1);
-        if (r == -1) {
+        if (r < 0) {
             if (errno == EINTR)
                 continue;
             else
@@ -391,7 +391,7 @@ void ifch_main(void)
         umask(022);
         resolv_conf_fd = open(resolv_conf_d, O_RDWR | O_CREAT, 644);
         umask(077);
-        if (resolv_conf_fd == -1) {
+        if (resolv_conf_fd < 0) {
             suicide("FATAL - unable to open resolv.conf");
         }
     }
diff --git a/ndhc/ifset.c b/ndhc/ifset.c
index 8f1e64c..0d57ba1 100644
--- a/ndhc/ifset.c
+++ b/ndhc/ifset.c
@@ -315,10 +315,10 @@ static int link_flags_get(int fd, uint32_t *flags)
 
     do {
         ret = nl_recv_buf(fd, nlbuf, sizeof nlbuf);
-        if (ret == -1)
+        if (ret < 0)
             return -2;
         if (nl_foreach_nlmsg(nlbuf, ret, seq, 0, link_flags_get_do,
-                             &ipx) == -1)
+                             &ipx) < 0)
             return -3;
     } while (ret > 0);
     if (ipx.got_flags) {
@@ -424,10 +424,10 @@ static int ipbcpfx_clear_others(int fd, uint32_t ipaddr, uint32_t bcast,
 
     do {
         ret = nl_recv_buf(fd, nlbuf, sizeof nlbuf);
-        if (ret == -1)
+        if (ret < 0)
             return -2;
         if (nl_foreach_nlmsg(nlbuf, ret, seq, 0,
-                             ipbcpfx_clear_others_do, &ipx) == -1)
+                             ipbcpfx_clear_others_do, &ipx) < 0)
             return -3;
     } while (ret > 0);
     return ipx.already_ok ? 1 : 0;
diff --git a/ndhc/ndhc.c b/ndhc/ndhc.c
index 21b5c39..860f465 100644
--- a/ndhc/ndhc.c
+++ b/ndhc/ndhc.c
@@ -264,7 +264,7 @@ static void do_ndhc_work(void)
     int timeout;
 
     cs.epollFd = epoll_create1(0);
-    if (cs.epollFd == -1)
+    if (cs.epollFd < 0)
         suicide("epoll_create1 failed");
 
     if (enforce_seccomp_ndhc())
@@ -280,7 +280,7 @@ static void do_ndhc_work(void)
 
     for (;;) {
         int r = epoll_wait(cs.epollFd, events, NDHC_NUM_EP_FDS, timeout);
-        if (r == -1) {
+        if (r < 0) {
             if (errno == EINTR)
                 continue;
             else
@@ -306,7 +306,7 @@ static void do_ndhc_work(void)
             nowts = curms();
             long long arp_wake_ts = arp_get_wake_ts();
             long long dhcp_wake_ts = dhcp_get_wake_ts();
-            if (arp_wake_ts == -1) {
+            if (arp_wake_ts < 0) {
                 if (dhcp_wake_ts != -1) {
                     timeout = dhcp_wake_ts - nowts;
                     if (timeout < 0)
@@ -417,7 +417,7 @@ static void ndhc_main(void) {
         suicide("%s: failed to open netlink socket", __func__);
 
     if (client_config.foreground && !client_config.background_if_no_lease) {
-        if (file_exists(pidfile, "w") == -1)
+        if (file_exists(pidfile, "w") < 0)
             suicide("%s: can't open pidfile '%s' for write!",
                     __func__, pidfile);
         write_pid(pidfile);
@@ -440,12 +440,12 @@ void background(void)
     static char called;
     if (!called) {
         called = 1;  // Do not fork again.
-        if (daemon(0, 0) == -1) {
+        if (daemon(0, 0) < 0) {
             perror("fork");
             exit(EXIT_SUCCESS);
         }
     }
-    if (file_exists(pidfile, "w") == -1) {
+    if (file_exists(pidfile, "w") < 0) {
         log_warning("Cannot open pidfile for write!");
     } else
         write_pid(pidfile);
@@ -486,7 +486,7 @@ static void parse_program_options(int argc, char *argv[])
         int c;
         c = getopt_long(argc, argv, "c:bp:P:h:i:nqr:V:u:U:D:C:s:Sdw:W:m:M:t:R:Hv?",
                         arg_options, NULL);
-        if (c == -1) break;
+        if (c < 0) break;
 
         switch (c) {
             case 'c':
diff --git a/ndhc/netlink.c b/ndhc/netlink.c
index 9836990..1a1cca5 100644
--- a/ndhc/netlink.c
+++ b/ndhc/netlink.c
@@ -92,10 +92,10 @@ void handle_nl_message(struct client_state_t *cs)
     assert(cs->nlFd != -1);
     do {
         ret = nl_recv_buf(cs->nlFd, nlbuf, sizeof nlbuf);
-        if (ret == -1)
+        if (ret < 0)
             break;
         if (nl_foreach_nlmsg(nlbuf, ret, 0, cs->nlPortId, nl_process_msgs, cs)
-            == -1)
+            < 0)
             break;
     } while (ret > 0);
 }
@@ -147,10 +147,10 @@ static int handle_getifdata(int fd, uint32_t seq)
     int got_ifdata = 0;
     do {
         ret = nl_recv_buf(fd, nlbuf, sizeof nlbuf);
-        if (ret == -1)
+        if (ret < 0)
             return -1;
         if (nl_foreach_nlmsg(nlbuf, ret, seq, 0,
-                             do_handle_getifdata, &got_ifdata) == -1)
+                             do_handle_getifdata, &got_ifdata) < 0)
             return -1;
     } while (ret > 0);
     return got_ifdata ? 0 : -1;
@@ -183,7 +183,7 @@ int nl_getifdata(void)
         pr = poll(&((struct pollfd){.fd=fd,.events=POLLIN}), 1, -1);
         if (pr == 1)
             ret = handle_getifdata(fd, seq);
-        else if (pr == -1 && errno != EINTR)
+        else if (pr < 0 && errno != EINTR)
             goto fail_fd;
     }
   fail_fd:
diff --git a/ndhc/nl.c b/ndhc/nl.c
index 3d5866d..2c154f5 100644
--- a/ndhc/nl.c
+++ b/ndhc/nl.c
@@ -96,7 +96,7 @@ ssize_t nl_recv_buf(int fd, char *buf, size_t blen)
     ssize_t ret;
   retry:
     ret = recvmsg(fd, &msg, MSG_DONTWAIT);
-    if (ret == -1) {
+    if (ret < 0) {
         if (errno == EINTR)
             goto retry;
         if (errno != EAGAIN && errno != EWOULDBLOCK) {
@@ -264,11 +264,11 @@ int nl_open(int nltype, int nlgroup, int *nlportid)
 {
     int fd;
     fd = socket(AF_NETLINK, SOCK_RAW, nltype);
-    if (fd == -1) {
+    if (fd < 0) {
         log_error("%s: socket failed: %s", __func__, strerror(errno));
         return -1;
     }
-    if (fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK) == -1) {
+    if (fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK) < 0) {
         log_error("%s: Set non-blocking failed: %s",
                   __func__, strerror(errno));
         goto err_close;
@@ -283,13 +283,13 @@ int nl_open(int nltype, int nlgroup, int *nlportid)
         .nl_family = AF_NETLINK,
         .nl_groups = nlgroup,
     };
-    if (bind(fd, (struct sockaddr *)&nlsock, sizeof nlsock) == -1) {
+    if (bind(fd, (struct sockaddr *)&nlsock, sizeof nlsock) < 0) {
         log_error("%s: bind to group failed: %s",
                   __func__, strerror(errno));
         goto err_close;
     }
     al = sizeof nlsock;
-    if (getsockname(fd, (struct sockaddr *)&nlsock, &al) == -1) {
+    if (getsockname(fd, (struct sockaddr *)&nlsock, &al) < 0) {
         log_error("%s: getsockname failed: %s",
                   __func__, strerror(errno));
         goto err_close;
diff --git a/ndhc/sockd.c b/ndhc/sockd.c
index 1b1e041..4b6d02b 100644
--- a/ndhc/sockd.c
+++ b/ndhc/sockd.c
@@ -120,19 +120,19 @@ int request_sockd_fd(char *buf, size_t buflen, char *response)
 static int create_arp_socket(void)
 {
     int fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ARP));
-    if (fd == -1) {
+    if (fd < 0) {
         log_error("%s: (%s) socket failed: %s", client_config.interface,
                   __func__, strerror(errno));
         goto out;
     }
 
     int opt = 1;
-    if (setsockopt(fd, SOL_SOCKET, SO_BROADCAST, &opt, sizeof opt) == -1) {
+    if (setsockopt(fd, SOL_SOCKET, SO_BROADCAST, &opt, sizeof opt) < 0) {
         log_error("%s: (%s) setsockopt failed: %s", client_config.interface,
                   __func__, strerror(errno));
         goto out_fd;
     }
-    if (fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK) == -1) {
+    if (fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK) < 0) {
         log_error("%s: (%s) fcntl failed: %s", client_config.interface,
                   __func__, strerror(errno));
         goto out_fd;
@@ -164,12 +164,12 @@ static int create_udp_socket(uint32_t ip, uint16_t port, char *iface)
         goto out;
     }
     int opt = 1;
-    if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof opt) == -1) {
+    if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof opt) < 0) {
         log_error("%s: (%s) Set reuse addr failed: %s",
                   client_config.interface, __func__, strerror(errno));
         goto out_fd;
     }
-    if (setsockopt(fd, SOL_SOCKET, SO_DONTROUTE, &opt, sizeof opt) == -1) {
+    if (setsockopt(fd, SOL_SOCKET, SO_DONTROUTE, &opt, sizeof opt) < 0) {
         log_error("%s: (%s) Set don't route failed: %s",
                   client_config.interface, __func__, strerror(errno));
         goto out_fd;
@@ -187,7 +187,7 @@ static int create_udp_socket(uint32_t ip, uint16_t port, char *iface)
                   client_config.interface, __func__, strerror(errno));
         goto out_fd;
     }
-    if (fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK) == -1) {
+    if (fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK) < 0) {
         log_error("%s: (%s) Set non-blocking failed: %s",
                   client_config.interface, __func__, strerror(errno));
         goto out_fd;
@@ -198,7 +198,7 @@ static int create_udp_socket(uint32_t ip, uint16_t port, char *iface)
         .sin_port = htons(port),
         .sin_addr.s_addr = ip,
     };
-    if (bind(fd, (struct sockaddr *)&sa, sizeof sa) == -1)
+    if (bind(fd, (struct sockaddr *)&sa, sizeof sa) < 0)
         goto out_fd;
 
     return fd;
@@ -225,12 +225,12 @@ static int create_raw_socket(struct sockaddr_ll *sa, bool *using_bpf,
     }
 
     int opt = 1;
-    if (setsockopt(fd, SOL_SOCKET, SO_DONTROUTE, &opt, sizeof opt) == -1) {
+    if (setsockopt(fd, SOL_SOCKET, SO_DONTROUTE, &opt, sizeof opt) < 0) {
         log_error("create_raw_socket: Failed to set don't route: %s",
                   strerror(errno));
         goto out_fd;
     }
-    if (fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK) == -1) {
+    if (fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK) < 0) {
         log_error("create_raw_socket: Set non-blocking failed: %s",
                   strerror(errno));
         goto out_fd;
@@ -252,10 +252,10 @@ static int create_udp_listen_socket(void)
 {
     int fd = create_udp_socket(INADDR_ANY, DHCP_CLIENT_PORT,
                                client_config.interface);
-    if (fd == -1)
+    if (fd < 0)
         return -1;
     int opt = 1;
-    if (setsockopt(fd, SOL_SOCKET, SO_BROADCAST, &opt, sizeof opt) == -1) {
+    if (setsockopt(fd, SOL_SOCKET, SO_BROADCAST, &opt, sizeof opt) < 0) {
         log_error("%s: (%s) Set broadcast failed: %s",
                   client_config.interface, __func__, strerror(errno));
         close(fd);
@@ -590,7 +590,7 @@ static void process_client_pipe(void)
 static void do_sockd_work(void)
 {
     epollfd = epoll_create1(0);
-    if (epollfd == -1)
+    if (epollfd < 0)
         suicide("epoll_create1 failed");
 
     if (enforce_seccomp_sockd())
@@ -601,7 +601,7 @@ static void do_sockd_work(void)
 
     for (;;) {
         int r = epoll_wait(epollfd, events, 2, -1);
-        if (r == -1) {
+        if (r < 0) {
             if (errno == EINTR)
                 continue;
             else
diff --git a/ndhc/state.c b/ndhc/state.c
index 3ebac06..01c87ef 100644
--- a/ndhc/state.c
+++ b/ndhc/state.c
@@ -246,7 +246,7 @@ static void an_packet(struct client_state_t *cs, struct dhcpmsg *packet,
             inet_ntop(AF_INET, &(struct in_addr){.s_addr=cs->clientAddr},
                       clibuf, sizeof clibuf);
             log_line("Accepted a firm offer for %s.  Validating...", clibuf);
-            if (arp_check(cs, packet) == -1) {
+            if (arp_check(cs, packet) < 0) {
                 log_warning("Failed to make arp socket.  Searching for new lease...");
                 reinit_selecting(cs, 3000);
             }
diff --git a/ndhc/sys.c b/ndhc/sys.c
index f1da9d0..2efbb81 100644
--- a/ndhc/sys.c
+++ b/ndhc/sys.c
@@ -41,7 +41,7 @@ void epoll_add(int epfd, int fd)
     ev.events = EPOLLIN | EPOLLRDHUP | EPOLLERR | EPOLLHUP;
     ev.data.fd = fd;
     r = epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &ev);
-    if (r == -1)
+    if (r < 0)
         suicide("epoll_add failed %s", strerror(errno));
 }
 
@@ -52,6 +52,6 @@ void epoll_del(int epfd, int fd)
     ev.events = EPOLLIN | EPOLLRDHUP | EPOLLERR | EPOLLHUP;
     ev.data.fd = fd;
     r = epoll_ctl(epfd, EPOLL_CTL_DEL, fd, &ev);
-    if (r == -1)
+    if (r < 0)
         suicide("epoll_del failed %s", strerror(errno));
 }