diff --git a/src/OT/glyf/Glyph.hh b/src/OT/glyf/Glyph.hh
index 155a4b5d3..9834acefc 100644
--- a/src/OT/glyf/Glyph.hh
+++ b/src/OT/glyf/Glyph.hh
@@ -93,15 +93,15 @@ struct Glyph
     float topSideY = all_points[len - 2].y;
     float bottomSideY = all_points[len - 1].y;
 
-    unsigned hori_aw = roundf (rightSideX - leftSideX);
+    signed hori_aw = roundf (rightSideX - leftSideX);
     if (hori_aw < 0) hori_aw = 0;
     int lsb = roundf (xMin - leftSideX);
-    plan->hmtx_map.set (new_gid, hb_pair (hori_aw, lsb));
+    plan->hmtx_map.set (new_gid, hb_pair ((unsigned) hori_aw, lsb));
 
-    unsigned vert_aw = roundf (topSideY - bottomSideY);
+    signed vert_aw = roundf (topSideY - bottomSideY);
     if (vert_aw < 0) vert_aw = 0;
     int tsb = roundf (topSideY - yMax);
-    plan->vmtx_map.set (new_gid, hb_pair (vert_aw, tsb));
+    plan->vmtx_map.set (new_gid, hb_pair ((unsigned) vert_aw, tsb));
   }
 
   bool compile_header_bytes (const hb_subset_plan_t *plan,