--- a/src/http/modules/ngx_http_ssl_module.c
+++ b/src/http/modules/ngx_http_ssl_module.c
@@ -338,7 +338,8 @@ ngx_http_ssl_alpn_select(ngx_ssl_conn_t 
 #if (NGX_DEBUG)
     for (i = 0; i < inlen; i += in[i] + 1) {
         ngx_log_debug2(NGX_LOG_DEBUG_HTTP, c->log, 0,
-                       "SSL ALPN supported by client: %*s", in[i], &in[i + 1]);
+                       "SSL ALPN supported by client: %*s",
+                       (size_t) in[i], &in[i + 1]);
     }
 #endif
 
@@ -365,7 +366,7 @@ ngx_http_ssl_alpn_select(ngx_ssl_conn_t 
     }
 
     ngx_log_debug2(NGX_LOG_DEBUG_HTTP, c->log, 0,
-                   "SSL ALPN selected: %*s", *outlen, *out);
+                   "SSL ALPN selected: %*s", (size_t) *outlen, *out);
 
     return SSL_TLSEXT_ERR_OK;
 }