diff --git a/lib/source-map-generator.js b/lib/source-map-generator.js
index 8111e061..f20344ae 100644
--- a/lib/source-map-generator.js
+++ b/lib/source-map-generator.js
@@ -9,7 +9,7 @@ const base64VLQ = require("./base64-vlq");
 const util = require("./util");
 const ArraySet = require("./array-set").ArraySet;
 const MappingList = require("./mapping-list").MappingList;
-
+const BasicSourceMapConsumer = require("./source-map-consumer").BasicSourceMapConsumer;
 /**
  * An instance of the SourceMapGenerator represents a source map which is
  * being built incrementally. You may pass an object with the following
@@ -200,11 +200,19 @@ class SourceMapGenerator {
     // Find mappings for the "sourceFile"
     this._mappings.unsortedForEach(function(mapping) {
       if (mapping.source === sourceFile && mapping.originalLine != null) {
+        
         // Check if it can be mapped by the source map, then update the mapping.
-        const original = aSourceMapConsumer.originalPositionFor({
+        let generatedPosition = {
           line: mapping.originalLine,
-          column: mapping.originalColumn
-        });
+          column: mapping.originalColumn,
+          bias: BasicSourceMapConsumer.GREATEST_LOWER_BOUND
+        };
+        let original = aSourceMapConsumer.originalPositionFor(generatedPosition);
+        if (original.source === null) {
+          generatedPosition.bias = BasicSourceMapConsumer.LEAST_UPPER_BOUND;
+          original = aSourceMapConsumer.originalPositionFor(generatedPosition);
+        }
+
         if (original.source != null) {
           // Copy mapping
           mapping.source = original.source;