diff --git a/lib/less/parser/parser.js b/lib/less/parser/parser.js
index cd7c7222..df309789 100644
--- a/lib/less/parser/parser.js
+++ b/lib/less/parser/parser.js
@@ -92,14 +92,23 @@ var Parser = function Parser(context, imports, fileInfo) {
         // @param [additionalData] An optional map which can contains vars - a map (key, value) of variables to apply
         //
         parse: function (str, callback, additionalData) {
-            var root, error = null, globalVars, modifyVars, preText = "";
+            var root, error = null, globalVars, modifyVars, ignored, preText = "";
 
             globalVars = (additionalData && additionalData.globalVars) ? Parser.serializeVars(additionalData.globalVars) + '\n' : '';
             modifyVars = (additionalData && additionalData.modifyVars) ? '\n' + Parser.serializeVars(additionalData.modifyVars) : '';
 
+            if (context.pluginManager) {
+                var preProcessors = context.pluginManager.getPreProcessors();
+                for (var i = 0; i < preProcessors.length; i++) {
+                    str = preProcessors[i].process(str, { context: context, imports: imports, fileInfo: fileInfo });
+                }
+            }
+
             if (globalVars || (additionalData && additionalData.banner)) {
                 preText = ((additionalData && additionalData.banner) ? additionalData.banner : "") + globalVars;
-                imports.contentsIgnoredChars[fileInfo.filename] = preText.length;
+                ignored = imports.contentsIgnoredChars;
+                ignored[fileInfo.filename] = ignored[fileInfo.filename] || 0;
+                ignored[fileInfo.filename] += preText.length;
             }
 
             str = str.replace(/\r\n?/g, '\n');
diff --git a/lib/less/plugin-manager.js b/lib/less/plugin-manager.js
index abae2f1c..8f6df7c7 100644
--- a/lib/less/plugin-manager.js
+++ b/lib/less/plugin-manager.js
@@ -4,6 +4,7 @@
 var PluginManager = function(less) {
     this.less = less;
     this.visitors = [];
+    this.preProcessors = [];
     this.postProcessors = [];
     this.installedPlugins = [];
     this.fileManagers = [];
@@ -35,6 +36,20 @@ PluginManager.prototype.addPlugin = function(plugin) {
 PluginManager.prototype.addVisitor = function(visitor) {
     this.visitors.push(visitor);
 };
+/**
+ * Adds a pre processor object
+ * @param {object} preProcessor
+ * @param {number} priority - guidelines 1 = before import, 1000 = import, 2000 = after import
+ */
+PluginManager.prototype.addPreProcessor = function(preProcessor, priority) {
+    var indexToInsertAt;
+    for (indexToInsertAt = 0; indexToInsertAt < this.preProcessors.length; indexToInsertAt++) {
+        if (this.preProcessors[indexToInsertAt].priority >= priority) {
+            break;
+        }
+    }
+    this.preProcessors.splice(indexToInsertAt, 0, {preProcessor: preProcessor, priority: priority});
+};
 /**
  * Adds a post processor object
  * @param {object} postProcessor
@@ -56,6 +71,18 @@ PluginManager.prototype.addPostProcessor = function(postProcessor, priority) {
 PluginManager.prototype.addFileManager = function(manager) {
     this.fileManagers.push(manager);
 };
+/**
+ *
+ * @returns {Array}
+ * @private
+ */
+PluginManager.prototype.getPreProcessors = function() {
+    var preProcessors = [];
+    for (var i = 0; i < this.preProcessors.length; i++) {
+        preProcessors.push(this.preProcessors[i].preProcessor);
+    }
+    return preProcessors;
+};
 /**
  *
  * @returns {Array}
diff --git a/lib/less/source-map-builder.js b/lib/less/source-map-builder.js
index 5163a88d..ee28041e 100644
--- a/lib/less/source-map-builder.js
+++ b/lib/less/source-map-builder.js
@@ -30,8 +30,12 @@ module.exports = function (SourceMapOutput, environment) {
     };
 
     SourceMapBuilder.prototype.getCSSAppendage = function() {
+
         var sourceMapURL = this.sourceMapURL;
         if (this.options.sourceMapFileInline) {
+            if (this.sourceMap === undefined) {
+                return "";
+            }
             sourceMapURL = "data:application/json;base64," + environment.encodeBase64(this.sourceMap);
         }
 
diff --git a/test/index.js b/test/index.js
index c58e1e19..7a858d67 100644
--- a/test/index.js
+++ b/test/index.js
@@ -40,6 +40,7 @@ lessTester.runTestSet({strictMath: true, strictUnits: true, sourceMap: true, glo
         }
         return path.join('test/sourcemaps', filename) + '.json';
     });
+lessTester.runTestSet({strictMath: true, strictUnits: true, sourceMap: {sourceMapFileInline: true}}, "sourcemaps-empty/", lessTester.testEmptySourcemap);
 lessTester.runTestSet({globalVars: true, banner: "/**\n  * Test\n  */\n"}, "globalVars/",
     null, null, null, function(name, type, baseFolder) { return path.join(baseFolder, name) + '.json'; });
 lessTester.runTestSet({modifyVars: true}, "modifyVars/",
@@ -49,4 +50,4 @@ lessTester.runTestSet({paths: ['test/data/', 'test/less/import/']}, "include-pat
 lessTester.testSyncronous({syncImport: true}, "import");
 lessTester.testSyncronous({syncImport: true}, "css");
 lessTester.testNoOptions();
-lessTester.finished();
\ No newline at end of file
+lessTester.finished();
diff --git a/test/less-test.js b/test/less-test.js
index ba142418..b90d58de 100644
--- a/test/less-test.js
+++ b/test/less-test.js
@@ -89,6 +89,23 @@ module.exports = function() {
         });
     }
 
+    function testEmptySourcemap(name, err, compiledLess, doReplacements, sourcemap, baseFolder) {
+        process.stdout.write("- " + path.join(baseFolder, name) + ": ");
+        if (err) {
+            fail("ERROR: " + (err && err.message));
+        } else {
+            var expectedSourcemap = undefined;
+            if ( compiledLess !== "" ) {
+                difference("\nCompiledLess must be empty", "", compiledLess);
+
+            } else if (sourcemap !== expectedSourcemap) {
+                fail("Sourcemap must be undefined");
+            } else {
+                ok('OK');
+            }
+        }
+    }
+
     function testErrors(name, err, compiledLess, doReplacements, sourcemap, baseFolder) {
         fs.readFile(path.join(baseFolder, name) + '.txt', 'utf8', function (e, expectedErr) {
             process.stdout.write("- " + path.join(baseFolder, name) + ": ");
@@ -189,7 +206,7 @@ module.exports = function() {
 
             totalTests++;
 
-            if (options.sourceMap) {
+            if (options.sourceMap && !options.sourceMap.sourceMapFileInline) {
                 options.sourceMapOutputFilename = name + ".css";
                 options.sourceMapBasepath = path.join(process.cwd(), baseFolder);
                 options.sourceMapRootpath = "testweb/";
@@ -247,10 +264,10 @@ module.exports = function() {
     function diff(left, right) {
         require('diff').diffLines(left, right).forEach(function(item) {
             if (item.added || item.removed) {
-                var text = item.value.replace("\n", String.fromCharCode(182) + "\n").replace('\ufeff', '[[BOM]]');
+                var text = item.value && item.value.replace("\n", String.fromCharCode(182) + "\n").replace('\ufeff', '[[BOM]]');
                 process.stdout.write(stylize(text, item.added ? 'green' : 'red'));
             } else {
-                process.stdout.write(item.value.replace('\ufeff', '[[BOM]]'));
+                process.stdout.write(item.value && item.value.replace('\ufeff', '[[BOM]]'));
             }
         });
         process.stdout.write("\n");
@@ -352,6 +369,7 @@ module.exports = function() {
         testSyncronous: testSyncronous,
         testErrors: testErrors,
         testSourcemap: testSourcemap,
+        testEmptySourcemap: testEmptySourcemap,
         testNoOptions: testNoOptions,
         prepBomTest: prepBomTest,
         finished: finished
diff --git a/test/less/sourcemaps-empty/empty.less b/test/less/sourcemaps-empty/empty.less
new file mode 100644
index 00000000..e69de29b
diff --git a/test/less/sourcemaps-empty/var-defs.less b/test/less/sourcemaps-empty/var-defs.less
new file mode 100644
index 00000000..19465415
--- /dev/null
+++ b/test/less/sourcemaps-empty/var-defs.less
@@ -0,0 +1 @@
+@test-var: 'something';
\ No newline at end of file