diff --git a/src/drawer.js b/src/drawer.js
index 248266ba..34cf3506 100644
--- a/src/drawer.js
+++ b/src/drawer.js
@@ -404,6 +404,7 @@ function updateViewport( drawer ) {
         viewportBR = rotatedBounds.getBottomRight();
     }
     else if (degrees !== 0) {
+        // This is just an approximation.
         var orthBounds = viewportBounds.rotate(90);
         viewportBounds.x -= orthBounds.width / 2;
         viewportBounds.y -= orthBounds.height / 2;
diff --git a/src/navigator.js b/src/navigator.js
index d07a2bba..9e18d6ca 100644
--- a/src/navigator.js
+++ b/src/navigator.js
@@ -241,7 +241,7 @@ $.extend( $.Navigator.prototype, $.EventSource.prototype, $.Viewer.prototype, /*
                     (this.container.clientHeight === 0 ? 1 : this.container.clientHeight)
                 );
             if ( !containerSize.equals( this.oldContainerSize ) ) {
-                var oldBounds = this.viewport.getBounds().rotate(this.viewport.degrees);
+                var oldBounds = this.viewport.getBounds();
                 var oldCenter = this.viewport.getCenter();
                 this.viewport.resize( containerSize, true );
                 var imageHeight = 1 / this.source.aspectRatio;
diff --git a/src/rectangle.js b/src/rectangle.js
index b518190e..1bac049f 100644
--- a/src/rectangle.js
+++ b/src/rectangle.js
@@ -195,6 +195,11 @@ $.Rect.prototype = /** @lends OpenSeadragon.Rect.prototype */{
 
         degrees = ( degrees + 360 ) % 360;
 
+        if (degrees % 90 !== 0)
+        {
+            throw new Error('Currently only 0, 90, 180, and 270 degrees are supported.');
+        }
+
         if( degrees === 0 ){
             return new $.Rect(
                 this.x,