diff --git a/src/hb-ot-font.cc b/src/hb-ot-font.cc
index c4ec612c88c0402a4abf03aa8169c8d4b6b7b8bc..f84dbc285448d1cfc507799db27d0e756e6a2142 100644
--- a/src/hb-ot-font.cc
+++ b/src/hb-ot-font.cc
@@ -50,7 +50,7 @@ struct hb_ot_face_metrics_accelerator_t
   unsigned short line_gap;
   bool has_font_extents;
 
-  const OT::_mtx *table;
+  const OT::hmtxvmtx *table;
   hb_blob_t *blob;
 
   inline void init (hb_face_t *face,
@@ -91,7 +91,7 @@ struct hb_ot_face_metrics_accelerator_t
 
     this->has_font_extents = got_font_extents;
 
-    this->blob = OT::Sanitizer<OT::_mtx>::sanitize (face->reference_table (_mtx_tag));
+    this->blob = OT::Sanitizer<OT::hmtxvmtx>::sanitize (face->reference_table (_mtx_tag));
 
     /* Cap num_metrics() and num_advances() based on table length. */
     unsigned int len = hb_blob_get_length (this->blob);
@@ -107,7 +107,7 @@ struct hb_ot_face_metrics_accelerator_t
       hb_blob_destroy (this->blob);
       this->blob = hb_blob_get_empty ();
     }
-    this->table = OT::Sanitizer<OT::_mtx>::lock_instance (this->blob);
+    this->table = OT::Sanitizer<OT::hmtxvmtx>::lock_instance (this->blob);
   }
 
   inline void fini (void)
diff --git a/src/hb-ot-hmtx-table.hh b/src/hb-ot-hmtx-table.hh
index a9606b3d27f01da2e8ddf99d66f16cf536294526..30aa625347f4f33ae95d5f2e0130f10f8ae36c7e 100644
--- a/src/hb-ot-hmtx-table.hh
+++ b/src/hb-ot-hmtx-table.hh
@@ -50,10 +50,8 @@ struct LongMetric
   DEFINE_SIZE_STATIC (4);
 };
 
-struct _mtx
+struct hmtxvmtx
 {
-  static const hb_tag_t tableTag = HB_TAG('_','m','t','x');
-
   static const hb_tag_t hmtxTag	= HB_OT_TAG_hmtx;
   static const hb_tag_t vmtxTag	= HB_OT_TAG_vmtx;
 
@@ -91,10 +89,10 @@ struct _mtx
   DEFINE_SIZE_ARRAY2 (0, longMetric, leadingBearingX);
 };
 
-struct hmtx : _mtx {
+struct hmtx : hmtxvmtx {
   static const hb_tag_t tableTag	= HB_OT_TAG_hmtx;
 };
-struct vmtx : _mtx {
+struct vmtx : hmtxvmtx {
   static const hb_tag_t tableTag	= HB_OT_TAG_vmtx;
 };