diff --git a/src/hb-common.cc b/src/hb-common.cc
index 41229b9..7266d9b 100644
--- a/src/hb-common.cc
+++ b/src/hb-common.cc
@@ -160,7 +160,7 @@
 
 /* hb_direction_t */
 
-const char direction_strings[][4] = {
+static const char direction_strings[][4] = {
   "ltr",
   "rtl",
   "ttb",