diff --git a/lib/consolidate.js b/lib/consolidate.js
index 0b8d60b..a198484 100644
--- a/lib/consolidate.js
+++ b/lib/consolidate.js
@@ -114,13 +114,13 @@ function read(path, options, cb) {
 
 function readPartials(path, options, cb) {
   if (!options.partials) return cb();
-  var partials = options.partials;
-  var keys = Object.keys(partials);
+  var keys = Object.keys(options.partials);
+  var partials = {};
 
   function next(index) {
-    if (index === keys.length) return cb(null);
+    if (index === keys.length) return cb(null, partials);
     var key = keys[index];
-    var partialPath = partials[key];
+    var partialPath = options.partials[key];
 
     if (partialPath === undefined || partialPath === null || partialPath === false) {
       return next(++index);
@@ -139,7 +139,7 @@ function readPartials(path, options, cb) {
 
     read(file, options, function(err, str) {
       if (err) return cb(err);
-      options.partials[key] = str;
+      partials[key] = str;
       next(++index);
     });
   }
@@ -171,14 +171,17 @@ function fromStringRenderer(name) {
     options.filename = path;
 
     return promisify(cb, function(cb) {
-      readPartials(path, options, function(err) {
+      readPartials(path, options, function(err, partials) {
+        var extend = (requires.extend || (requires.extend = require('util')._extend));
+        var opts = extend({}, options);
+        opts.partials = partials;
         if (err) return cb(err);
-        if (cache(options)) {
-          exports[name].render('', options, cb);
+        if (cache(opts)) {
+          exports[name].render('', opts, cb);
         } else {
-          read(path, options, function(err, str) {
+          read(path, opts, function(err, str) {
             if (err) return cb(err);
-            exports[name].render(str, options, cb);
+            exports[name].render(str, opts, cb);
           });
         }
       });
@@ -894,9 +897,11 @@ exports.underscore.render = function(str, options, cb) {
   return promisify(cb, function(cb) {
     var engine = requires.underscore || (requires.underscore = require('underscore'));
     try {
+      const partials = {};
       for (var partial in options.partials) {
-        options.partials[partial] = engine.template(options.partials[partial]);
+        partials[partial] = engine.template(options.partials[partial]);
       }
+      options.partials = partials;
       var tmpl = cache(options) || cache(options, engine.template(str, null, options));
       cb(null, tmpl(options).replace(/\n$/, ''));
     } catch (err) {