diff --git a/src/js/app-bar.jsx b/src/js/app-bar.jsx
index 80cec78d427db7..3a686327511bb5 100644
--- a/src/js/app-bar.jsx
+++ b/src/js/app-bar.jsx
@@ -47,7 +47,7 @@ var AppBar = React.createClass({
     if (this.props.title) {
       // If the title is a string, wrap in an h1 tag.
       // If not, just use it as a node.
-      title = toString.call(this.props.title) === '[object String]' ?
+      title = Object.prototype.toString.call(this.props.title) === '[object String]' ?
         <h1 className="mui-app-bar-title">{this.props.title}</h1> :
         this.props.title;
     }
diff --git a/src/js/dialog.jsx b/src/js/dialog.jsx
index af08c2958fbc04..ea91c64e9d6955 100644
--- a/src/js/dialog.jsx
+++ b/src/js/dialog.jsx
@@ -21,7 +21,7 @@ var Dialog = React.createClass({
     if (this.props.title) {
       // If the title is a string, wrap in an h3 tag.
       // If not, just use it as a node.
-      title = toString.call(this.props.title) === '[object String]' ?
+      title = Object.prototype.toString.call(this.props.title) === '[object String]' ?
         <h3 className="mui-dialog-title">{this.props.title}</h3> :
         this.props.title;
     }