diff --git a/src/http/ngx_http_spdy.c b/src/http/ngx_http_spdy.c
index 3febc23e9..acadaf232 100644
--- a/src/http/ngx_http_spdy.c
+++ b/src/http/ngx_http_spdy.c
@@ -2176,7 +2176,7 @@ ngx_http_spdy_handle_request_header(ngx_http_request_t *r)
 
 
 void
-ngx_http_spdy_request_headers_init()
+ngx_http_spdy_request_headers_init(void)
 {
     ngx_uint_t                       i;
     ngx_http_spdy_request_header_t  *h;
diff --git a/src/http/ngx_http_spdy.h b/src/http/ngx_http_spdy.h
index 4294e3d50..63014066d 100644
--- a/src/http/ngx_http_spdy.h
+++ b/src/http/ngx_http_spdy.h
@@ -186,7 +186,7 @@ ngx_http_spdy_queue_blocked_frame(ngx_http_spdy_connection_t *sc,
 
 
 void ngx_http_spdy_init(ngx_event_t *rev);
-void ngx_http_spdy_request_headers_init();
+void ngx_http_spdy_request_headers_init(void);
 
 ngx_int_t ngx_http_spdy_read_request_body(ngx_http_request_t *r,
     ngx_http_client_body_handler_pt post_handler);
diff --git a/src/os/unix/ngx_darwin_init.c b/src/os/unix/ngx_darwin_init.c
index e3cc5fe3e..1bc7520ca 100644
--- a/src/os/unix/ngx_darwin_init.c
+++ b/src/os/unix/ngx_darwin_init.c
@@ -59,7 +59,7 @@ sysctl_t sysctls[] = {
 
 
 void
-ngx_debug_init()
+ngx_debug_init(void)
 {
 #if (NGX_DEBUG_MALLOC)
 
diff --git a/src/os/unix/ngx_freebsd_init.c b/src/os/unix/ngx_freebsd_init.c
index aeeceaf25..c4c12dd74 100644
--- a/src/os/unix/ngx_freebsd_init.c
+++ b/src/os/unix/ngx_freebsd_init.c
@@ -72,7 +72,7 @@ sysctl_t sysctls[] = {
 
 
 void
-ngx_debug_init()
+ngx_debug_init(void)
 {
 #if (NGX_DEBUG_MALLOC)
 
diff --git a/src/os/unix/ngx_freebsd_rfork_thread.c b/src/os/unix/ngx_freebsd_rfork_thread.c
index 530ec4a53..e92f9a9fd 100644
--- a/src/os/unix/ngx_freebsd_rfork_thread.c
+++ b/src/os/unix/ngx_freebsd_rfork_thread.c
@@ -271,7 +271,7 @@ ngx_init_threads(int n, size_t size, ngx_cycle_t *cycle)
 
 
 ngx_tid_t
-ngx_thread_self()
+ngx_thread_self(void)
 {
     ngx_int_t  tid;
 
diff --git a/src/os/unix/ngx_freebsd_rfork_thread.h b/src/os/unix/ngx_freebsd_rfork_thread.h
index 2c238f79c..ff160449d 100644
--- a/src/os/unix/ngx_freebsd_rfork_thread.h
+++ b/src/os/unix/ngx_freebsd_rfork_thread.h
@@ -57,7 +57,7 @@ extern size_t   ngx_thread_stack_size;
 
 
 static ngx_inline ngx_int_t
-ngx_gettid()
+ngx_gettid(void)
 {
     char  *sp;
 
@@ -83,7 +83,7 @@ ngx_gettid()
 }
 
 
-ngx_tid_t ngx_thread_self();
+ngx_tid_t ngx_thread_self(void);
 
 
 typedef ngx_uint_t               ngx_tls_key_t;