diff --git a/expat/ConfigureChecks.cmake b/expat/ConfigureChecks.cmake
index 3fc732f0..a7ba25a6 100644
--- a/expat/ConfigureChecks.cmake
+++ b/expat/ConfigureChecks.cmake
@@ -57,7 +57,7 @@ check_c_source_compiles("
         #include <stdlib.h>  /* for NULL */
         #include <unistd.h>  /* for syscall */
         #include <sys/syscall.h>  /* for SYS_getrandom */
-        int main() {
+        int main(void) {
             syscall(SYS_getrandom, NULL, 0, 0);
             return 0;
         }"
diff --git a/expat/configure.ac b/expat/configure.ac
index 04415e36..ddfd818d 100644
--- a/expat/configure.ac
+++ b/expat/configure.ac
@@ -215,7 +215,7 @@ AC_LINK_IFELSE([AC_LANG_SOURCE([
     #else
     # include <stdlib.h>  /* for arc4random_buf on BSD */
     #endif
-    int main() {
+    int main(void) {
       char dummy[[123]];  // double brackets for m4
       arc4random_buf(dummy, 0U);
       return 0;
@@ -232,7 +232,7 @@ AC_LINK_IFELSE([AC_LANG_SOURCE([
        #else
        # include <stdlib.h>
        #endif
-       int main() {
+       int main(void) {
           arc4random();
           return 0;
        }
@@ -254,7 +254,7 @@ AS_IF([test "x$with_getrandom" != xno],
    AC_LINK_IFELSE([AC_LANG_SOURCE([
        #include <stdlib.h>  /* for NULL */
        #include <sys/random.h>
-       int main() {
+       int main(void) {
          return getrandom(NULL, 0U, 0U);
        }
      ])],
@@ -278,7 +278,7 @@ AS_IF([test "x$with_sys_getrandom" != xno],
        #include <stdlib.h>  /* for NULL */
        #include <unistd.h>  /* for syscall */
        #include <sys/syscall.h>  /* for SYS_getrandom */
-       int main() {
+       int main(void) {
          syscall(SYS_getrandom, NULL, 0, 0);
          return 0;
      }
diff --git a/expat/gennmtab/gennmtab.c b/expat/gennmtab/gennmtab.c
index c6152cf3..82cfccff 100644
--- a/expat/gennmtab/gennmtab.c
+++ b/expat/gennmtab/gennmtab.c
@@ -442,7 +442,7 @@ printTabs(char *tab) {
 }
 
 int
-main() {
+main(void) {
   char tab[2 * 65536];
   memset(tab, 0, 65536);
   setTab(tab, nmstrt, sizeof(nmstrt) / sizeof(nmstrt[0]));