diff --git a/src/unix/lwt_unix_stubs.c b/src/unix/lwt_unix_stubs.c
index a8eedde87..443773bac 100644
--- a/src/unix/lwt_unix_stubs.c
+++ b/src/unix/lwt_unix_stubs.c
@@ -465,10 +465,11 @@ static void lwt_unix_socketpair(int domain, int type, int protocol,
   uerror("socketpair", Nothing);
 }
 
-static int socket_domain_table[] = {PF_UNIX, PF_INET, PF_INET6};
+static const int socket_domain_table[] =
+  {PF_UNIX, PF_INET, PF_INET6};
 
-static int socket_type_table[] = {SOCK_STREAM, SOCK_DGRAM, SOCK_RAW,
-                                  SOCK_SEQPACKET};
+static const int socket_type_table[] =
+  {SOCK_STREAM, SOCK_DGRAM, SOCK_RAW, SOCK_SEQPACKET};
 
 CAMLprim value lwt_unix_socketpair_stub(value cloexec, value domain, value type,
                                         value protocol) {
diff --git a/src/unix/unix_c/unix_access_job.c b/src/unix/unix_c/unix_access_job.c
index a054fc34c..0a607686e 100644
--- a/src/unix/unix_c/unix_access_job.c
+++ b/src/unix/unix_c/unix_access_job.c
@@ -34,7 +34,7 @@
    +-----------------------------------------------------------------+ */
 
 /* Table mapping constructors of ocaml type Unix.access_permission to C values. */
-static int access_permission_table[] = {
+static const int access_permission_table[] = {
   /* Constructor R_OK. */
   R_OK,
   /* Constructor W_OK. */
diff --git a/src/unix/unix_c/unix_getaddrinfo_job.c b/src/unix/unix_c/unix_getaddrinfo_job.c
index 395335d15..d7b1f8d0d 100644
--- a/src/unix/unix_c/unix_getaddrinfo_job.c
+++ b/src/unix/unix_c/unix_getaddrinfo_job.c
@@ -29,7 +29,7 @@ struct job_getaddrinfo {
     char data[];
 };
 
-static value cst_to_constr(int n, int *tbl, int size, int deflt)
+static value cst_to_constr(int n, const int *tbl, int size, int deflt)
 {
     int i;
     for (i = 0; i < size; i++)
@@ -37,7 +37,7 @@ static value cst_to_constr(int n, int *tbl, int size, int deflt)
     return Val_int(deflt);
 }
 
-static value convert_addrinfo(struct addrinfo *a)
+static value convert_addrinfo(const struct addrinfo *a)
 {
     CAMLparam0();
     CAMLlocal3(vres, vaddr, vcanonname);
diff --git a/src/unix/unix_c/unix_getnameinfo_job.c b/src/unix/unix_c/unix_getnameinfo_job.c
index 3ae74091d..8f5e3bbdb 100644
--- a/src/unix/unix_c/unix_getnameinfo_job.c
+++ b/src/unix/unix_c/unix_getnameinfo_job.c
@@ -28,8 +28,8 @@ struct job_getnameinfo {
     int result;
 };
 
-static int getnameinfo_flag_table[] = {NI_NOFQDN, NI_NUMERICHOST, NI_NAMEREQD,
-                                       NI_NUMERICSERV, NI_DGRAM};
+static const int getnameinfo_flag_table[] =
+  {NI_NOFQDN, NI_NUMERICHOST, NI_NAMEREQD, NI_NUMERICSERV, NI_DGRAM};
 
 static void worker_getnameinfo(struct job_getnameinfo *job)
 {
diff --git a/src/unix/unix_c/unix_lockf_job.c b/src/unix/unix_c/unix_lockf_job.c
index a0449d80f..67732f8b0 100644
--- a/src/unix/unix_c/unix_lockf_job.c
+++ b/src/unix/unix_c/unix_lockf_job.c
@@ -84,8 +84,8 @@ static void worker_lockf(struct job_lockf *job)
 
 #else
 
-static int lock_command_table[] = {F_ULOCK, F_LOCK, F_TLOCK,
-                                   F_TEST,  F_LOCK, F_TLOCK};
+static const int lock_command_table[] =
+  {F_ULOCK, F_LOCK, F_TLOCK, F_TEST,  F_LOCK, F_TLOCK};
 
 static void worker_lockf(struct job_lockf *job)
 {
diff --git a/src/unix/unix_c/unix_lseek_job.c b/src/unix/unix_c/unix_lseek_job.c
index fe2740493..291611a84 100644
--- a/src/unix/unix_c/unix_lseek_job.c
+++ b/src/unix/unix_c/unix_lseek_job.c
@@ -35,7 +35,7 @@
    +-----------------------------------------------------------------+ */
 
 /* Table mapping constructors of ocaml type Unix.seek_command to C values. */
-static int seek_command_table[] = {
+static const int seek_command_table[] = {
   /* Constructor SEEK_SET. */
   SEEK_SET,
   /* Constructor SEEK_CUR. */
diff --git a/src/unix/unix_c/unix_madvise.c b/src/unix/unix_c/unix_madvise.c
index f619a4441..51b1d3ce9 100644
--- a/src/unix/unix_c/unix_madvise.c
+++ b/src/unix/unix_c/unix_madvise.c
@@ -12,7 +12,7 @@
 #include <caml/bigarray.h>
 #include <sys/mman.h>
 
-static int advise_table[] = {
+static const int advise_table[] = {
     MADV_NORMAL, MADV_RANDOM, MADV_SEQUENTIAL, MADV_WILLNEED, MADV_DONTNEED,
 #if defined(MADV_MERGEABLE)
 	MADV_MERGEABLE,
diff --git a/src/unix/unix_c/unix_open_job.c b/src/unix/unix_c/unix_open_job.c
index a77ad1cab..0c1be8459 100644
--- a/src/unix/unix_c/unix_open_job.c
+++ b/src/unix/unix_c/unix_open_job.c
@@ -35,7 +35,7 @@
 #define caml_unix_cloexec_default unix_cloexec_default
 #endif
 
-static int open_flag_table[] = {
+static const int open_flag_table[] = {
     O_RDONLY, O_WRONLY, O_RDWR,  O_NONBLOCK, O_APPEND, O_CREAT, O_TRUNC,
     O_EXCL,   O_NOCTTY, O_DSYNC, O_SYNC,     O_RSYNC,  0, /* O_SHARE_DELETE,
                                                              Windows-only */
diff --git a/src/unix/unix_c/unix_recv_send_utils.c b/src/unix/unix_c/unix_recv_send_utils.c
index f9486afe9..bbb3d9c1f 100644
--- a/src/unix/unix_c/unix_recv_send_utils.c
+++ b/src/unix/unix_c/unix_recv_send_utils.c
@@ -19,7 +19,7 @@
 
 #include "unix_recv_send_utils.h"
 
-int msg_flag_table[3] = {MSG_OOB, MSG_DONTROUTE, MSG_PEEK};
+const int msg_flag_table[3] = {MSG_OOB, MSG_DONTROUTE, MSG_PEEK};
 
 value wrapper_recv_msg(int fd, int n_iovs, struct iovec *iovs)
 {
diff --git a/src/unix/unix_c/unix_recv_send_utils.h b/src/unix/unix_c/unix_recv_send_utils.h
index f4b9bd76d..407091f6e 100644
--- a/src/unix/unix_c/unix_recv_send_utils.h
+++ b/src/unix/unix_c/unix_recv_send_utils.h
@@ -36,9 +36,15 @@
 #define caml_unix_socket_type_table socket_type_table
 #endif
 
-extern int msg_flag_table[];
+#if OCAML_VERSION < 50300
 extern int caml_unix_socket_domain_table[];
 extern int caml_unix_socket_type_table[];
+#else
+extern const int caml_unix_socket_domain_table[];
+extern const int caml_unix_socket_type_table[];
+#endif
+
+extern const int msg_flag_table[];
 extern void get_sockaddr(value mladdr, union sock_addr_union *addr /*out*/,
                          socklen_t *addr_len /*out*/);
 value wrapper_recv_msg(int fd, int n_iovs, struct iovec *iovs);
diff --git a/src/unix/unix_c/unix_tcflow_job.c b/src/unix/unix_c/unix_tcflow_job.c
index 764fe3c57..24042b80c 100644
--- a/src/unix/unix_c/unix_tcflow_job.c
+++ b/src/unix/unix_c/unix_tcflow_job.c
@@ -35,7 +35,7 @@
    +-----------------------------------------------------------------+ */
 
 /* Table mapping constructors of ocaml type Unix.flow_action to C values. */
-static int flow_action_table[] = {
+static const int flow_action_table[] = {
   /* Constructor TCOOFF. */
   TCOOFF,
   /* Constructor TCOON. */
diff --git a/src/unix/unix_c/unix_tcflush_job.c b/src/unix/unix_c/unix_tcflush_job.c
index 9287ca8e8..d76bf1ee1 100644
--- a/src/unix/unix_c/unix_tcflush_job.c
+++ b/src/unix/unix_c/unix_tcflush_job.c
@@ -35,7 +35,7 @@
    +-----------------------------------------------------------------+ */
 
 /* Table mapping constructors of ocaml type Unix.flush_queue to C values. */
-static int flush_queue_table[] = {
+static const int flush_queue_table[] = {
   /* Constructor TCIFLUSH. */
   TCIFLUSH,
   /* Constructor TCOFLUSH. */
diff --git a/src/unix/unix_c/unix_tcsetattr_job.c b/src/unix/unix_c/unix_tcsetattr_job.c
index b699b5069..9d3029db2 100644
--- a/src/unix/unix_c/unix_tcsetattr_job.c
+++ b/src/unix/unix_c/unix_tcsetattr_job.c
@@ -24,7 +24,7 @@ struct job_tcsetattr {
     int error_code;
 };
 
-static int when_flag_table[] = {TCSANOW, TCSADRAIN, TCSAFLUSH};
+static const int when_flag_table[] = {TCSANOW, TCSADRAIN, TCSAFLUSH};
 
 static void worker_tcsetattr(struct job_tcsetattr *job)
 {
diff --git a/src/unix/unix_c/unix_termios_conversion.c b/src/unix/unix_c/unix_termios_conversion.c
index e9b82f8e6..cee17025f 100644
--- a/src/unix/unix_c/unix_termios_conversion.c
+++ b/src/unix/unix_c/unix_termios_conversion.c
@@ -20,7 +20,7 @@ enum { Iflags, Oflags, Cflags, Lflags };
 
 /* Structure of the terminal_io record. Cf. unix.mli */
 
-static long terminal_io_descr[] = {
+static const long terminal_io_descr[] = {
     /* Input modes */
     Bool, Iflags, IGNBRK, Bool, Iflags, BRKINT, Bool, Iflags, IGNPAR, Bool,
     Iflags, PARMRK, Bool, Iflags, INPCK, Bool, Iflags, ISTRIP, Bool, Iflags,
@@ -40,7 +40,7 @@ static long terminal_io_descr[] = {
     Char, VINTR, Char, VQUIT, Char, VERASE, Char, VKILL, Char, VEOF, Char, VEOL,
     Char, VMIN, Char, VTIME, Char, VSTART, Char, VSTOP, End};
 
-static struct {
+static const struct {
     speed_t speed;
     int baud;
 } speedtable[] = {{B50, 50},
@@ -152,10 +152,7 @@ static tcflag_t *choose_field(struct termios *terminal_status, long field)
 
 void encode_terminal_status(struct termios *terminal_status, volatile value *dst)
 {
-    long *pc;
-    int i;
-
-    for (pc = terminal_io_descr; *pc != End; dst++) {
+    for (const long *pc = terminal_io_descr; *pc != End; dst++) {
         switch (*pc++) {
             case Bool: {
                 tcflag_t *src = choose_field(terminal_status, *pc++);
@@ -168,7 +165,7 @@ void encode_terminal_status(struct termios *terminal_status, volatile value *dst
                 int ofs = *pc++;
                 int num = *pc++;
                 tcflag_t msk = *pc++;
-                for (i = 0; i < num; i++) {
+                for (int i = 0; i < num; i++) {
                     if ((*src & msk) == pc[i]) {
                         *dst = Val_int(i + ofs);
                         break;
@@ -190,7 +187,7 @@ void encode_terminal_status(struct termios *terminal_status, volatile value *dst
                         speed = cfgetispeed(terminal_status);
                         break;
                 }
-                for (i = 0; i < NSPEEDS; i++) {
+                for (int i = 0; i < NSPEEDS; i++) {
                     if (speed == speedtable[i].speed) {
                         *dst = Val_int(speedtable[i].baud);
                         break;
@@ -209,10 +206,7 @@ void encode_terminal_status(struct termios *terminal_status, volatile value *dst
 
 int decode_terminal_status(struct termios *terminal_status, volatile value *src)
 {
-    long *pc;
-    int i;
-
-    for (pc = terminal_io_descr; *pc != End; src++) {
+    for (const long *pc = terminal_io_descr; *pc != End; src++) {
         switch (*pc++) {
             case Bool: {
                 tcflag_t *dst = choose_field(terminal_status, *pc++);
@@ -228,7 +222,7 @@ int decode_terminal_status(struct termios *terminal_status, volatile value *src)
                 int ofs = *pc++;
                 int num = *pc++;
                 tcflag_t msk = *pc++;
-                i = Int_val(*src) - ofs;
+                int i = Int_val(*src) - ofs;
                 if (i >= 0 && i < num) {
                     *dst = (*dst & ~msk) | pc[i];
                 } else {
@@ -242,7 +236,7 @@ int decode_terminal_status(struct termios *terminal_status, volatile value *src)
                 int which = *pc++;
                 int baud = Int_val(*src);
                 int res = 0;
-                for (i = 0; i < NSPEEDS; i++) {
+                for (int i = 0; i < NSPEEDS; i++) {
                     if (baud == speedtable[i].baud) {
                         switch (which) {
                             case Output:
diff --git a/src/unix/unix_c/unix_wait4.c b/src/unix/unix_c/unix_wait4.c
index daa9ab4f4..eae1aa6ad 100644
--- a/src/unix/unix_c/unix_wait4.c
+++ b/src/unix/unix_c/unix_wait4.c
@@ -58,7 +58,7 @@ static value alloc_process_status(int status)
     return st;
 }
 
-static int wait_flag_table[] = {WNOHANG, WUNTRACED};
+static const int wait_flag_table[] = {WNOHANG, WUNTRACED};
 
 value lwt_unix_wait4(value flags, value pid_req)
 {