diff --git a/src/OT/Layout/Common/CoverageFormat2.hh b/src/OT/Layout/Common/CoverageFormat2.hh
index 43b56fe15..ea14be16f 100644
--- a/src/OT/Layout/Common/CoverageFormat2.hh
+++ b/src/OT/Layout/Common/CoverageFormat2.hh
@@ -95,10 +95,14 @@ struct CoverageFormat2_4
     unsigned count = 0;
     unsigned range = (unsigned) -1;
     last = (hb_codepoint_t) -2;
+    unsigned unsorted = false;
     for (auto g: glyphs)
     {
       if (last + 1 != g)
       {
+	if (unlikely (last != (hb_codepoint_t) -2 && last + 1 > g))
+	  unsorted = true;
+
         range++;
         rangeRecord.arrayZ[range].first = g;
         rangeRecord.arrayZ[range].value = count;
@@ -107,7 +111,9 @@ struct CoverageFormat2_4
       last = g;
       count++;
     }
-    rangeRecord.as_array ().qsort (RangeRecord<Types>::cmp_range); // To handle unsorted glyph order.
+
+    if (unlikely (unsorted))
+      rangeRecord.as_array ().qsort (RangeRecord<Types>::cmp_range);
 
     return_trace (true);
   }
diff --git a/src/hb-ot-layout-common.hh b/src/hb-ot-layout-common.hh
index b229bdcee..36f123b55 100644
--- a/src/hb-ot-layout-common.hh
+++ b/src/hb-ot-layout-common.hh
@@ -1769,6 +1769,7 @@ struct ClassDefFormat2_4
       return_trace (true);
     }
 
+    unsigned unsorted = false;
     unsigned num_ranges = 1;
     hb_codepoint_t prev_gid = (*it).first;
     unsigned prev_klass = (*it).second;
@@ -1789,6 +1790,10 @@ struct ClassDefFormat2_4
       if (cur_gid != prev_gid + 1 ||
 	  cur_klass != prev_klass)
       {
+
+	if (unlikely (cur_gid < prev_gid))
+	  unsorted = true;
+
 	if (unlikely (!record)) break;
 	record->last = prev_gid;
 	num_ranges++;
@@ -1808,7 +1813,9 @@ struct ClassDefFormat2_4
 
     if (likely (record)) record->last = prev_gid;
     rangeRecord.len = num_ranges;
-    rangeRecord.as_array ().qsort (RangeRecord<Types>::cmp_range); // To handle unsorted glyph order.
+
+    if (unlikely (unsorted))
+      rangeRecord.as_array ().qsort (RangeRecord<Types>::cmp_range);
 
     return_trace (true);
   }