Fixed: generate source maps when they are actually requested.

lib/loader.js

@@ -19,10 +19,12 @@ module.exports = function(content, map) {
 	var sourceMap = query.sourceMap || false;
 	var resolve = createResolver(query.alias);
 
-	if(sourceMap && map !== null && typeof map !== "string") {
-		map = JSON.stringify(map);
+	if(sourceMap) {
+		if (map && typeof map !== "string") {
+			map = JSON.stringify(map);
+		}
 	} else {
-        // Some loaders (example `postcss-loader: 1`) always generate source map, we should remove their
+		// Some loaders (example `"postcss-loader": "1.x.x"`) always generates source map, we should remove it
 		map = null;
 	}
 
@@ -32,7 +34,8 @@ module.exports = function(content, map) {
 		to: loaderUtils.getCurrentRequest(this),
 		query: query,
 		minimize: this.minimize,
-		loaderContext: this
+		loaderContext: this,
+		sourceMap: sourceMap
 	}, function(err, result) {
 		if(err) return callback(err);
 

lib/processCss.js

@@ -200,12 +200,12 @@ module.exports = function processCss(inputSource, inputMap, options, callback) {
 		// we need a prefix to avoid path rewriting of PostCSS
 		from: "/css-loader!" + options.from,
 		to: options.to,
-		map: {
+		map: options.sourceMap ? {
 			prev: inputMap,
 			sourcesContent: true,
 			inline: false,
 			annotation: false
-		}
+		} : null
 	}).then(function(result) {
 		callback(null, {
 			source: result.css,