diff --git a/auto/cc/sunc b/auto/cc/sunc
index 226ef5ea6..806ccc439 100644
--- a/auto/cc/sunc
+++ b/auto/cc/sunc
@@ -20,7 +20,10 @@ have=NGX_COMPILER value="\"Sun C $NGX_SUNC_VER\"" . auto/define
 
 cat << END > $NGX_AUTOTEST.c
 
-int main() { printf("%d", __SUNPRO_C); }
+int main(void) {
+    printf("%d", __SUNPRO_C);
+    return 0;
+}
 
 END
 
diff --git a/auto/endianness b/auto/endianness
index 70b0a106c..1b552b6b3 100644
--- a/auto/endianness
+++ b/auto/endianness
@@ -15,7 +15,7 @@ END
 
 cat << END > $NGX_AUTOTEST.c
 
-int main() {
+int main(void) {
     int i = 0x11223344;
     char *p;
 
diff --git a/auto/feature b/auto/feature
index 1145f2868..3561f5941 100644
--- a/auto/feature
+++ b/auto/feature
@@ -31,7 +31,7 @@ cat << END > $NGX_AUTOTEST.c
 $NGX_INCLUDE_UNISTD_H
 $ngx_feature_incs
 
-int main() {
+int main(void) {
     $ngx_feature_test;
     return 0;
 }
diff --git a/auto/include b/auto/include
index e34dabdae..0f8bc1e04 100644
--- a/auto/include
+++ b/auto/include
@@ -20,7 +20,7 @@ cat << END > $NGX_AUTOTEST.c
 $NGX_INCLUDE_SYS_PARAM_H
 #include <$ngx_include>
 
-int main() {
+int main(void) {
     return 0;
 }
 
diff --git a/auto/types/sizeof b/auto/types/sizeof
index b5b71bb98..480d8cfa4 100644
--- a/auto/types/sizeof
+++ b/auto/types/sizeof
@@ -25,7 +25,7 @@ $NGX_INCLUDE_UNISTD_H
 $NGX_INCLUDE_INTTYPES_H
 $NGX_INCLUDE_AUTO_CONFIG_H
 
-int main() {
+int main(void) {
     printf("%d", (int) sizeof($ngx_type));
     return 0;
 }
diff --git a/auto/types/typedef b/auto/types/typedef
index b55237e93..d54c28978 100644
--- a/auto/types/typedef
+++ b/auto/types/typedef
@@ -27,7 +27,7 @@ do
 #include <netinet/in.h>
 $NGX_INCLUDE_INTTYPES_H
 
-int main() {
+int main(void) {
     $ngx_try i = 0;
     return (int) i;
 }
diff --git a/auto/types/uintptr_t b/auto/types/uintptr_t
index 2b7212ebe..7db6e4506 100644
--- a/auto/types/uintptr_t
+++ b/auto/types/uintptr_t
@@ -19,7 +19,7 @@ cat << END > $NGX_AUTOTEST.c
 #include <sys/types.h>
 $NGX_INTTYPES_H
 
-int main() {
+int main(void) {
     uintptr_t i = 0;
     return (int) i;
 }