diff --git a/lib/parser.js b/lib/parser.js
index c43b6f5..cc9b086 100644
--- a/lib/parser.js
+++ b/lib/parser.js
@@ -406,10 +406,10 @@ module.exports = (function() {
     }
 
     function peg$computePosDetails(pos) {
-      function advance(details, pos) {
+      function advance(details, startPos, endPos) {
         var p, ch;
 
-        for (p = 0; p < pos; p++) {
+        for (p = startPos; p < endPos; p++) {
           ch = input.charAt(p);
           if (ch === "\n") {
             if (!details.seenCR) { details.line++; }
@@ -431,8 +431,8 @@ module.exports = (function() {
           peg$cachedPos = 0;
           peg$cachedPosDetails = { line: 1, column: 1, seenCR: false };
         }
+        advance(peg$cachedPosDetails, peg$cachedPos, pos);
         peg$cachedPos = pos;
-        advance(peg$cachedPosDetails, peg$cachedPos);
       }
 
       return peg$cachedPosDetails;