diff --git a/src/hb-ot-layout-gsub-table.hh b/src/hb-ot-layout-gsub-table.hh
index 05758ed79..f483d7526 100644
--- a/src/hb-ot-layout-gsub-table.hh
+++ b/src/hb-ot-layout-gsub-table.hh
@@ -1272,10 +1272,9 @@ struct SubstLookup : Lookup
     {
       /* The spec says all subtables of an Extension lookup should
        * have the same type, which shall not be the Extension type
-       * itself. This is specially important if one has a reverse type! */
+       * itself (but we already checked for that).
+       * This is specially important if one has a reverse type! */
       unsigned int type = get_subtable (0).u.extension.get_type ();
-      if (unlikely (type == SubstLookupSubTable::Extension))
-	return_trace (false);
       unsigned int count = get_subtable_count ();
       for (unsigned int i = 1; i < count; i++)
         if (get_subtable (i).u.extension.get_type () != type)
diff --git a/src/hb-ot-layout-gsubgpos-private.hh b/src/hb-ot-layout-gsubgpos-private.hh
index 0023b31c1..a5cb105ca 100644
--- a/src/hb-ot-layout-gsubgpos-private.hh
+++ b/src/hb-ot-layout-gsubgpos-private.hh
@@ -2230,7 +2230,9 @@ struct ExtensionFormat1
   inline bool sanitize (hb_sanitize_context_t *c) const
   {
     TRACE_SANITIZE (this);
-    return_trace (c->check_struct (this) && extensionOffset != 0);
+    return_trace (c->check_struct (this) &&
+		  extensionOffset != 0 &&
+		  extensionLookupType != T::LookupSubTable::Extension);
   }
 
   protected: