diff --git a/polymer-overlay/polymer-overlay.html b/polymer-overlay/polymer-overlay.html
index dc20994..9259da3 100644
--- a/polymer-overlay/polymer-overlay.html
+++ b/polymer-overlay/polymer-overlay.html
@@ -248,6 +248,13 @@
 						focusOverlay();
 					}
 				},
+				positionTarget: function() {
+					var computedStyle = getComputedStyle(this.target);
+					if (this.opened && computedStyle.top === 'auto' && computedStyle.bottom === 'auto') {
+						this.target.style.width = (window.innerWidth - 20) + 'px';
+						this.target.style.top = ((window.innerHeight - this.target.getBoundingClientRect().height) / 2) + 'px';
+					}
+				},
 				renderOpened: function() {
 					this.target.classList.remove('closing');
 					this.target.classList.add('revealed');
@@ -256,6 +263,7 @@
 					this.asyncMethod('continueRenderOpened');
 				},
 				continueRenderOpened: function() {
+					this.positionTarget();
 					this.target.classList.toggle('opened', this.opened);
 					this.target.classList.toggle('closing', !this.opened);
 					this.animating = this.asyncMethod('completeOpening', null, this.timeout);