diff --git a/plugins/prefixIds.js b/plugins/prefixIds.js
index fd7b0ea66..74766cf64 100644
--- a/plugins/prefixIds.js
+++ b/plugins/prefixIds.js
@@ -164,14 +164,18 @@ exports.fn = function(node, opts, extra) {
         var idPrefixed = '';
         csstree.walk(cssAst, function(node) {
 
-            // #ID, .class
-            if ((node.type === 'IdSelector' ||
-                 node.type === 'ClassSelector') &&
-                 node.name) {
+            // #ID,
+            if (node.type === 'IdSelector' && node.name) {
                 node.name = addPrefix(node.name);
                 return;
             }
 
+            // .class
+            if (node.type === 'ClassSelector' && node.name) {
+                node.name = node.name.split(' ').map(addPrefix).join(' ');
+                return;
+            }
+
             // url(...) in value
             if (node.type === 'Url' &&
                 node.value.value && node.value.value.length > 0) {