diff --git a/TSRM/threads.m4 b/TSRM/threads.m4
index dc5719bbec056..c42b328dd6651 100644
--- a/TSRM/threads.m4
+++ b/TSRM/threads.m4
@@ -73,7 +73,7 @@ void *thread_routine(void *data) {
     return data;
 }
 
-int main() {
+int main(void) {
     pthread_t thd;
     pthread_mutexattr_t mattr;
     int data = 1;
diff --git a/Zend/Zend.m4 b/Zend/Zend.m4
index a1450e4f13396..c86aaaa4a7eb5 100644
--- a/Zend/Zend.m4
+++ b/Zend/Zend.m4
@@ -162,7 +162,7 @@ int stack_grows_downwards(uintptr_t arg) {
     return (uintptr_t)&local < arg;
 }
 
-int main() {
+int main(void) {
     int local;
 
     f = stack_grows_downwards;
@@ -250,7 +250,7 @@ typedef union _mm_align_test {
 #define ZEND_MM_ALIGNMENT (sizeof(mm_align_test))
 #endif
 
-int main()
+int main(void)
 {
   size_t i = ZEND_MM_ALIGNMENT;
   int zeros = 0;
diff --git a/build/php.m4 b/build/php.m4
index 4457af1d5e472..e11a00c3bcb16 100644
--- a/build/php.m4
+++ b/build/php.m4
@@ -1034,7 +1034,7 @@ AC_DEFUN([_PHP_CHECK_SIZEOF], [
 #endif
 $3
 
-int main()
+int main(void)
 {
 	FILE *fp = fopen("conftestval", "w");
 	if (!fp) return(1);
@@ -1102,7 +1102,7 @@ AC_CACHE_CHECK(for type of reentrant time-related functions, ac_cv_time_r_type,[
 AC_RUN_IFELSE([AC_LANG_SOURCE([[
 #include <time.h>
 
-int main() {
+int main(void) {
 char buf[27];
 struct tm t;
 time_t old = 0;
@@ -1118,7 +1118,7 @@ return (1);
 ],[
   AC_RUN_IFELSE([AC_LANG_SOURCE([[
 #include <time.h>
-int main() {
+int main(void) {
   struct tm t, *s;
   time_t old = 0;
   char buf[27], *p;
@@ -1159,7 +1159,7 @@ AC_DEFUN([PHP_DOES_PWRITE_WORK],[
 #include <errno.h>
 #include <stdlib.h>
 $1
-    int main() {
+    int main(void) {
     int fd = open("conftest_in", O_WRONLY|O_CREAT, 0600);
 
     if (fd < 0) return 1;
@@ -1193,7 +1193,7 @@ AC_DEFUN([PHP_DOES_PREAD_WORK],[
 #include <errno.h>
 #include <stdlib.h>
 $1
-    int main() {
+    int main(void) {
     char buf[3];
     int fd = open("conftest_in", O_RDONLY);
     if (fd < 0) return 1;
@@ -1405,7 +1405,7 @@ struct s
   int i;
   char c[1];
 };
-int main()
+int main(void)
 {
   struct s *s = malloc(sizeof(struct s) + 3);
   s->i = 3;
@@ -1463,7 +1463,7 @@ int seeker(void *cookie, off64_t *position, int whence)
 
 cookie_io_functions_t funcs = {reader, writer, seeker, closer};
 
-int main() {
+int main(void) {
   struct cookiedata g = { 0 };
   FILE *fp = fopencookie(&g, "r", funcs);
 
@@ -1590,7 +1590,7 @@ AC_DEFUN([PHP_CHECK_FUNC_LIB],[
   if test "$found" = "yes"; then
     ac_libs=$LIBS
     LIBS="$LIBS -l$2"
-    AC_RUN_IFELSE([AC_LANG_SOURCE([[int main() { return (0); }]])],[found=yes],[found=no],[
+    AC_RUN_IFELSE([AC_LANG_SOURCE([[int main(void) { return (0); }]])],[found=yes],[found=no],[
       dnl Cross compilation.
       found=yes
     ])
@@ -1644,7 +1644,7 @@ AC_DEFUN([PHP_TEST_BUILD], [
   AC_LINK_IFELSE([AC_LANG_SOURCE([[
     $5
     char $1();
-    int main() {
+    int main(void) {
       $1();
       return 0;
     }
@@ -2296,7 +2296,7 @@ AC_DEFUN([PHP_TEST_WRITE_STDOUT],[
 
 #define TEXT "This is the test message -- "
 
-int main()
+int main(void)
 {
   int n;
 
@@ -2818,7 +2818,7 @@ AC_DEFUN([PHP_CHECK_AVX512_SUPPORTS], [
 
   AC_LINK_IFELSE([AC_LANG_SOURCE([[
     #include <immintrin.h>
-      int main() {
+      int main(void) {
         __m512i mask = _mm512_set1_epi32(0x1);
         char out[32];
         _mm512_storeu_si512(out, _mm512_shuffle_epi8(mask, mask));
@@ -2846,7 +2846,7 @@ AC_DEFUN([PHP_CHECK_AVX512_VBMI_SUPPORTS], [
   CFLAGS="-mavx512f -mavx512cd -mavx512vl -mavx512dq -mavx512bw -mavx512vbmi $CFLAGS"
   AC_LINK_IFELSE([AC_LANG_SOURCE([[
     #include <immintrin.h>
-      int main() {
+      int main(void) {
         __m512i mask = _mm512_set1_epi32(0x1);
         char out[32];
         _mm512_storeu_si512(out, _mm512_permutexvar_epi8(mask, mask));
diff --git a/ext/iconv/config.m4 b/ext/iconv/config.m4
index ac57c81e7d472..3cf400fe96231 100644
--- a/ext/iconv/config.m4
+++ b/ext/iconv/config.m4
@@ -30,7 +30,8 @@ if test "$PHP_ICONV" != "no"; then
       AC_MSG_CHECKING([if using GNU libiconv])
       AC_RUN_IFELSE([AC_LANG_SOURCE([[
 #include <iconv.h>
-int main() {
+#include <stdio.h>
+int main(void) {
   printf("%d", _libiconv_version);
   return 0;
 }
@@ -90,7 +91,7 @@ int main() {
 #include <iconv.h>
 #include <errno.h>
 
-int main() {
+int main(void) {
   iconv_t cd;
   cd = iconv_open( "*blahblah*", "*blahblahblah*" );
   if (cd == (iconv_t)(-1)) {
@@ -117,7 +118,7 @@ int main() {
 #include <iconv.h>
 #include <stdlib.h>
 
-int main() {
+int main(void) {
   iconv_t cd = iconv_open( "UTF-8//IGNORE", "UTF-8" );
   if(cd == (iconv_t)-1) {
     return 1;
diff --git a/ext/opcache/config.m4 b/ext/opcache/config.m4
index 7e681bb112815..444ded9976ac1 100644
--- a/ext/opcache/config.m4
+++ b/ext/opcache/config.m4
@@ -116,7 +116,7 @@ if test "$PHP_OPCACHE" != "no"; then
 #include <unistd.h>
 #include <string.h>
 
-int main() {
+int main(void) {
   pid_t pid;
   int status;
   int ipc_id;
@@ -195,7 +195,7 @@ int main() {
 # define MAP_FAILED ((void*)-1)
 #endif
 
-int main() {
+int main(void) {
   pid_t pid;
   int status;
   char *shm;
@@ -257,7 +257,7 @@ int main() {
 # define MAP_FAILED ((void*)-1)
 #endif
 
-int main() {
+int main(void) {
   pid_t pid;
   int status;
   int fd;
diff --git a/ext/standard/config.m4 b/ext/standard/config.m4
index 87f41b25eb9d5..984dfcd8a256e 100644
--- a/ext/standard/config.m4
+++ b/ext/standard/config.m4
@@ -81,7 +81,7 @@ if test "$PHP_EXTERNAL_LIBCRYPT" != "no"; then
 #include <stdlib.h>
 #include <string.h>
 
-int main() {
+int main(void) {
 #if HAVE_CRYPT
 	char *encrypted = crypt("rasmuslerdorf","rl");
 	return !encrypted || strcmp(encrypted,"rl.3StKT.4T8M");
@@ -111,7 +111,7 @@ int main() {
 #include <stdlib.h>
 #include <string.h>
 
-int main() {
+int main(void) {
 #if HAVE_CRYPT
 	char *encrypted = crypt("rasmuslerdorf","_J9..rasm");
 	return !encrypted || strcmp(encrypted,"_J9..rasmBYk8r9AiWNc");
@@ -141,7 +141,7 @@ int main() {
 #include <stdlib.h>
 #include <string.h>
 
-int main() {
+int main(void) {
 #if HAVE_CRYPT
 	char salt[15], answer[40];
 	char *encrypted;
@@ -181,7 +181,7 @@ int main() {
 #include <stdlib.h>
 #include <string.h>
 
-int main() {
+int main(void) {
 #if HAVE_CRYPT
 	char salt[30], answer[70];
 	char *encrypted;
@@ -218,7 +218,7 @@ int main() {
 #include <stdlib.h>
 #include <string.h>
 
-int main() {
+int main(void) {
 #if HAVE_CRYPT
 	char salt[21], answer[21+86];
 	char *encrypted;
@@ -254,7 +254,7 @@ int main() {
 #include <stdlib.h>
 #include <string.h>
 
-int main() {
+int main(void) {
 #if HAVE_CRYPT
 	char salt[21], answer[21+43];
 	char *encrypted;
diff --git a/sapi/fpm/config.m4 b/sapi/fpm/config.m4
index ab85be7ca09aa..77dc32c56a908 100644
--- a/sapi/fpm/config.m4
+++ b/sapi/fpm/config.m4
@@ -66,7 +66,7 @@ AC_DEFUN([AC_FPM_CLOCK],
       #include <mach/clock.h>
       #include <mach/mach_error.h>
 
-      int main()
+      int main(void)
       {
         kern_return_t ret; clock_serv_t aClock; mach_timespec_t aTime;
         ret = host_get_clock_service(mach_host_self(), REALTIME_CLOCK, &aClock);
@@ -134,7 +134,7 @@ AC_DEFUN([AC_FPM_TRACE],
       #define PTRACE_PEEKDATA PT_READ_D
       #endif
 
-      int main()
+      int main(void)
       {
         long v1 = (unsigned int) -1; /* copy will fail if sizeof(long) == 8 and we've got "int ptrace()" */
         long v2;
@@ -239,7 +239,7 @@ AC_DEFUN([AC_FPM_TRACE],
       #include <sys/stat.h>
       #include <fcntl.h>
       #include <stdio.h>
-      int main()
+      int main(void)
       {
         long v1 = (unsigned int) -1, v2 = 0;
         char buf[128];
@@ -578,7 +578,7 @@ if test "$PHP_FPM" != "no"; then
     AC_CHECK_HEADERS([sys/acl.h])
 
     AC_COMPILE_IFELSE([AC_LANG_SOURCE([[#include <sys/acl.h>
-      int main()
+      int main(void)
       {
         acl_t acl;
         acl_entry_t user, group;
@@ -597,7 +597,7 @@ if test "$PHP_FPM" != "no"; then
           AC_MSG_RESULT([yes])
         ],[
           AC_RUN_IFELSE([AC_LANG_SOURCE([[#include <sys/acl.h>
-            int main()
+            int main(void)
             {
               acl_t acl;
               acl_entry_t user, group;