--- a/src/os/unix/ngx_os.h
+++ b/src/os/unix/ngx_os.h
@@ -24,9 +24,9 @@
 
 
 typedef struct {
-    ssize_t       (*recv)(ngx_connection_t *c, char *buf, size_t size);
+    ssize_t       (*recv)(ngx_connection_t *c, u_char *buf, size_t size);
     ssize_t       (*recv_chain)(ngx_connection_t *c, ngx_chain_t *in);
-    ssize_t       (*send)(ngx_connection_t *c, char *buf, size_t size);
+    ssize_t       (*send)(ngx_connection_t *c, u_char *buf, size_t size);
     ngx_chain_t  *(*send_chain)(ngx_connection_t *c, ngx_chain_t *in);
     int             flags;
 } ngx_os_io_t;
@@ -39,7 +39,7 @@ int ngx_posix_init(ngx_log_t *log);
 int ngx_posix_post_conf_init(ngx_log_t *log);
 
 
-ssize_t ngx_unix_recv(ngx_connection_t *c, char *buf, size_t size);
+ssize_t ngx_unix_recv(ngx_connection_t *c, u_char *buf, size_t size);
 ssize_t ngx_readv_chain(ngx_connection_t *c, ngx_chain_t *entry);
 ngx_chain_t *ngx_writev_chain(ngx_connection_t *c, ngx_chain_t *in);