diff --git a/av1/encoder/ethread.c b/av1/encoder/ethread.c
index 29d52ed..13f5b8a 100644
--- a/av1/encoder/ethread.c
+++ b/av1/encoder/ethread.c
@@ -160,8 +160,8 @@
   }
 }
 
-void assign_tile_to_thread(MultiThreadHandle *multi_thread_ctxt, int num_tiles,
-                           int num_workers) {
+static void assign_tile_to_thread(MultiThreadHandle *multi_thread_ctxt,
+                                  int num_tiles, int num_workers) {
   int tile_id = 0;
   int i;