diff --git a/lib/compiler.js b/lib/compiler.js
index 752d647..1dcdcc9 100644
--- a/lib/compiler.js
+++ b/lib/compiler.js
@@ -915,6 +915,10 @@ PEG.Compiler = {
       "    },",
       "    ",
       "    _matchFailed: function(failure) {",
+      "      if (this._pos < this._rightmostMatchFailuresPos) {",
+      "        return;",
+      "      }",
+      "      ",
       "      if (this._pos > this._rightmostMatchFailuresPos) {",
       "        this._rightmostMatchFailuresPos = this._pos;",
       "        this._rightmostMatchFailuresExpected = [];",
diff --git a/lib/metagrammar.js b/lib/metagrammar.js
index ea0b4d6..f1566c3 100644
--- a/lib/metagrammar.js
+++ b/lib/metagrammar.js
@@ -36,6 +36,10 @@ PEG.grammarParser = (function(){
     },
     
     _matchFailed: function(failure) {
+      if (this._pos < this._rightmostMatchFailuresPos) {
+        return;
+      }
+      
       if (this._pos > this._rightmostMatchFailuresPos) {
         this._rightmostMatchFailuresPos = this._pos;
         this._rightmostMatchFailuresExpected = [];