diff --git a/examples/deflate.c b/examples/deflate.c
index 63f3ea15..df1cb920 100644
--- a/examples/deflate.c
+++ b/examples/deflate.c
@@ -44,7 +44,7 @@ static void deflate(nghttp2_hd_deflater *deflater,
 static int inflate_header_block(nghttp2_hd_inflater *inflater, uint8_t *in,
                                 size_t inlen, int final);
 
-int main() {
+int main(void) {
   int rv;
   nghttp2_hd_deflater *deflater;
   nghttp2_hd_inflater *inflater;
diff --git a/tests/failmalloc.c b/tests/failmalloc.c
index 4bf83ca5..6294cfff 100644
--- a/tests/failmalloc.c
+++ b/tests/failmalloc.c
@@ -37,7 +37,7 @@ static int init_suite1(void) { return 0; }
 
 static int clean_suite1(void) { return 0; }
 
-int main() {
+int main(void) {
   CU_pSuite pSuite = NULL;
   unsigned int num_tests_failed;
 
diff --git a/tests/main.c b/tests/main.c
index 25cbbfd7..dc41c7c7 100644
--- a/tests/main.c
+++ b/tests/main.c
@@ -47,7 +47,7 @@ static int init_suite1(void) { return 0; }
 
 static int clean_suite1(void) { return 0; }
 
-int main() {
+int main(void) {
   CU_pSuite pSuite = NULL;
   unsigned int num_tests_failed;