diff --git a/src/libply/ply-region.c b/src/libply/ply-region.c
index 938be973..8c2e82e6 100644
--- a/src/libply/ply-region.c
+++ b/src/libply/ply-region.c
@@ -498,7 +498,7 @@ cover_with_rect(char             cover[COVER_SIZE][COVER_SIZE],
     }
 }
 
-int
+static int
 do_test (void)
 {
   ply_rectangle_t rectangle;