diff --git a/lib/source-map-consumer.js b/lib/source-map-consumer.js
index ee661146..d3c4b1a8 100644
--- a/lib/source-map-consumer.js
+++ b/lib/source-map-consumer.js
@@ -512,15 +512,15 @@ BasicSourceMapConsumer.prototype._parseMappings =
     var previousName = 0;
     var length = aStr.length;
     var index = 0;
-    var cachedSegments = {};
     var temp = {};
     var originalMappings = [];
     var generatedMappings = [];
-    var mapping, str, segment, end, value;
+    var mapping, segment, end, value, charCode;
 
     let subarrayStart = 0;
     while (index < length) {
-      if (aStr.charAt(index) === ';') {
+      charCode = aStr.charCodeAt(index);
+      if (charCode === 59) { // ';'
         generatedLine++;
         index++;
         previousGeneratedColumn = 0;
@@ -528,19 +528,20 @@ BasicSourceMapConsumer.prototype._parseMappings =
         sortGenerated(generatedMappings, subarrayStart);
         subarrayStart = generatedMappings.length;
       }
-      else if (aStr.charAt(index) === ',') {
+      else if (charCode === 44) { // ','
         index++;
       }
       else {
         mapping = new Mapping();
         mapping.generatedLine = generatedLine;
 
+        // Find end of segment (next ';' or ',')
         for (end = index; end < length; end++) {
-          if (this._charIsMappingSeparator(aStr, end)) {
+          charCode = aStr.charCodeAt(end);
+          if (charCode === 44 || charCode === 59) { // ',' or ';'
             break;
           }
         }
-        str = aStr.slice(index, end);
 
         segment = [];
         while (index < end) {