diff --git a/src/dhcp.c b/src/dhcp.c
index 3cf07cf..0514339 100644
--- a/src/dhcp.c
+++ b/src/dhcp.c
@@ -55,12 +55,12 @@ static int get_udp_unicast_socket(struct client_state_t cs[static 1])
     char buf[32];
     buf[0] = 'u';
     memcpy(buf + 1, &cs->clientAddr, sizeof cs->clientAddr);
-    return request_sockd_fd(buf, 1 + sizeof cs->clientAddr, NULL);
+    return request_sockd_fd(buf, 1 + sizeof cs->clientAddr, (char *)0);
 }
 
 static int get_raw_broadcast_socket(void)
 {
-    return request_sockd_fd("s", 1, NULL);
+    return request_sockd_fd("s", 1, (char *)0);
 }
 
 static int get_raw_listen_socket(struct client_state_t cs[static 1])
diff --git a/src/ifchd-parse.rl b/src/ifchd-parse.rl
index e37f9c4..7e604ed 100644
--- a/src/ifchd-parse.rl
+++ b/src/ifchd-parse.rl
@@ -109,7 +109,7 @@ static int perform_ip4set(const char buf[static 1], size_t len)
     }
 
     return perform_ip_subnet_bcast(ip4_addr, ip4_subnet,
-                                   have_bcast ? ip4_bcast : NULL);
+                                   have_bcast ? ip4_bcast : (char *)0);
 }
 
 %%{
diff --git a/src/ifset.c b/src/ifset.c
index 577d878..94012bf 100644
--- a/src/ifset.c
+++ b/src/ifset.c
@@ -426,8 +426,8 @@ static void ipbcpfx_clear_others_do(const struct nlmsghdr *nlh, void *data)
   erase:
     r = rtnl_addr_broadcast_send(ipx->fd, RTM_DELADDR, ifm->ifa_flags,
                                  ifm->ifa_scope,
-                                 tb[IFA_ADDRESS] ? RTA_DATA(tb[IFA_ADDRESS]) : NULL,
-                                 tb[IFA_BROADCAST] ? RTA_DATA(tb[IFA_BROADCAST]) : NULL,
+                                 tb[IFA_ADDRESS] ? RTA_DATA(tb[IFA_ADDRESS]) : (uint32_t *)0,
+                                 tb[IFA_BROADCAST] ? RTA_DATA(tb[IFA_BROADCAST]) : (uint32_t *)0,
                                  ifm->ifa_prefixlen);
     if (r < 0 && r != -2) {
         log_warning("%s: (%s) Failed to delete IP and broadcast addresses.",
diff --git a/src/ndhc.c b/src/ndhc.c
index a44b13a..3a4714b 100644
--- a/src/ndhc.c
+++ b/src/ndhc.c
@@ -166,7 +166,7 @@ static void setup_signals_ndhc(void)
     sigaddset(&mask, SIGUSR2);
     sigaddset(&mask, SIGCHLD);
     sigaddset(&mask, SIGTERM);
-    if (sigprocmask(SIG_BLOCK, &mask, NULL) < 0)
+    if (sigprocmask(SIG_BLOCK, &mask, (sigset_t *)0) < 0)
         suicide("sigprocmask failed");
     if (cs.signalFd >= 0) {
         epoll_del(cs.epollFd, cs.signalFd);
@@ -232,7 +232,7 @@ int get_clientid_string(const char str[static 1], size_t slen)
 
     uint8_t mac[6];
     for (size_t i = 0; i < sizeof mac; ++i)
-        mac[i] = strtol(str+i*3, NULL, 16);
+        mac[i] = strtol(str+i*3, (char **)0, 16);
     client_config.clientid[0] = 1; // Ethernet MAC type
     memcpy(client_config.clientid + 1, mac,
            min_size_t(sizeof mac, sizeof client_config.clientid - 1));
@@ -471,7 +471,7 @@ static void ndhc_main(void) {
 
     nk_set_chroot(chroot_dir);
     memset(chroot_dir, '\0', sizeof chroot_dir);
-    nk_set_uidgid(ndhc_uid, ndhc_gid, NULL, 0);
+    nk_set_uidgid(ndhc_uid, ndhc_gid, (const unsigned char *)0, 0);
 
     if (!carrier_isup()) {
         if (ifchange_deconfig(&cs) < 0)
diff --git a/src/sockd.c b/src/sockd.c
index e44b22a..ab2a066 100644
--- a/src/sockd.c
+++ b/src/sockd.c
@@ -319,7 +319,7 @@ static int create_raw_broadcast_socket(void)
         .sll_halen = 6,
     };
     memcpy(da.sll_addr, "\xff\xff\xff\xff\xff\xff", 6);
-    return create_raw_socket(&da, NULL, NULL);
+    return create_raw_socket(&da, (bool *)0, (struct sock_fprog *)0);
 }
 
 static bool arp_set_bpf_basic(int fd)
diff --git a/src/sys.c b/src/sys.c
index 8bdbfd6..548e4d8 100644
--- a/src/sys.c
+++ b/src/sys.c
@@ -77,7 +77,7 @@ int setup_signals_subprocess(void)
     sigaddset(&mask, SIGHUP);
     sigaddset(&mask, SIGINT);
     sigaddset(&mask, SIGTERM);
-    if (sigprocmask(SIG_BLOCK, &mask, NULL) < 0)
+    if (sigprocmask(SIG_BLOCK, &mask, (sigset_t *)0) < 0)
         suicide("sigprocmask failed");
     int sfd = signalfd(-1, &mask, SFD_NONBLOCK);
     if (sfd < 0)