Prefer C linkage
diff --git a/src/hb-unicode.c b/src/hb-unicode.c
index b237fbb..2de963e 100644
--- a/src/hb-unicode.c
+++ b/src/hb-unicode.c
@@ -28,6 +28,9 @@
 
 #include "hb-unicode-private.h"
 
+HB_BEGIN_DECLS
+
+
 /*
  * hb_unicode_funcs_t
  */
@@ -313,3 +316,6 @@
 
   return horiz_dir[script];
 }
+
+
+HB_END_DECLS