diff --git a/mongoose.c b/mongoose.c
index dc9345b5..a4070ec6 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -2570,8 +2570,8 @@ static void handle_file_request(struct mg_connection *conn, const char *path,
       "Connection: %s\r\n"
       "Accept-Ranges: bytes\r\n"
       "%s\r\n",
-      conn->request_info.status_code, msg, date, lm, etag,
-      mime_vec.len, mime_vec.ptr, cl, suggest_connection_header(conn), range);
+      conn->request_info.status_code, msg, date, lm, etag, (int) mime_vec.len,
+      mime_vec.ptr, cl, suggest_connection_header(conn), range);
 
   if (strcmp(conn->request_info.request_method, "HEAD") != 0) {
     send_file_data(conn, fp, cl);
diff --git a/mongoose.h b/mongoose.h
index 13632333..4ea1691f 100644
--- a/mongoose.h
+++ b/mongoose.h
@@ -160,7 +160,11 @@ int mg_write(struct mg_connection *, const void *buf, size_t len);
 // Note that mg_printf() uses internal buffer of size IO_BUF_SIZE
 // (8 Kb by default) as temporary message storage for formatting. Do not
 // print data that is bigger than that, otherwise it will be truncated.
-int mg_printf(struct mg_connection *, const char *fmt, ...);
+int mg_printf(struct mg_connection *, const char *fmt, ...)
+#ifdef __GNUC__
+__attribute__((format(printf, 2, 3)))
+#endif
+;
 
 
 // Send contents of the entire file together with HTTP headers.