diff --git a/src/hb-ft.cc b/src/hb-ft.cc
index d3c5d3db9..4537a8e6d 100644
--- a/src/hb-ft.cc
+++ b/src/hb-ft.cc
@@ -426,6 +426,7 @@ hb_ft_get_glyph_h_kerning (hb_font_t *font,
 			   void *user_data HB_UNUSED)
 {
   const hb_ft_font_t *ft_font = (const hb_ft_font_t *) font_data;
+  hb_lock_t lock (ft_font->lock);
   FT_Vector kerningv;
 
   FT_Kerning_Mode mode = font->x_ppem ? FT_KERNING_DEFAULT : FT_KERNING_UNFITTED;