diff --git a/src/ol/source/imagewms.js b/src/ol/source/imagewms.js
index b2c0f3b1ca..26eaa0bb41 100644
--- a/src/ol/source/imagewms.js
+++ b/src/ol/source/imagewms.js
@@ -189,41 +189,27 @@ ol.source.ImageWMS.prototype.getImageInternal = function(extent, resolution, pix
     pixelRatio = 1;
   }
 
-  extent = extent.slice();
-  var centerX = (extent[0] + extent[2]) / 2;
-  var centerY = (extent[1] + extent[3]) / 2;
-
   var imageResolution = resolution / pixelRatio;
-  var imageWidth = Math.ceil(ol.extent.getWidth(extent) / imageResolution);
-  var imageHeight = Math.ceil(ol.extent.getHeight(extent) / imageResolution);
 
-  var halfWidth = imageWidth * imageResolution / 2;
-  var halfHeight = imageHeight * imageResolution / 2;
-
-  extent[0] = centerX - halfWidth;
-  extent[1] = centerY - halfHeight;
-  extent[2] = centerX + halfWidth;
-  extent[3] = centerY + halfHeight;
+  var center = ol.extent.getCenter(extent);
+  var viewWidth = Math.ceil(ol.extent.getWidth(extent) / imageResolution);
+  var viewHeight = Math.ceil(ol.extent.getHeight(extent) / imageResolution);
+  var viewExtent = ol.extent.getForViewAndSize(center, resolution, 0,
+      [viewWidth, viewHeight]);
+  var requestWidth = Math.ceil(this.ratio_ * ol.extent.getWidth(extent) / imageResolution);
+  var requestHeight = Math.ceil(this.ratio_ * ol.extent.getHeight(extent) / imageResolution);
+  var requestExtent = ol.extent.getForViewAndSize(center, resolution, 0,
+      [requestWidth, requestHeight]);
 
   var image = this.image_;
   if (image &&
       this.renderedRevision_ == this.getRevision() &&
       image.getResolution() == resolution &&
       image.getPixelRatio() == pixelRatio &&
-      ol.extent.containsExtent(image.getExtent(), extent)) {
+      ol.extent.containsExtent(image.getExtent(), viewExtent)) {
     return image;
   }
 
-  if (this.ratio_ != 1) {
-    halfWidth *= this.ratio_;
-    halfHeight *= this.ratio_;
-
-    extent[0] = centerX - halfWidth;
-    extent[1] = centerY - halfHeight;
-    extent[2] = centerX + halfWidth;
-    extent[3] = centerY + halfHeight;
-  }
-
   var params = {
     'SERVICE': 'WMS',
     'VERSION': ol.DEFAULT_WMS_VERSION,
@@ -233,13 +219,13 @@ ol.source.ImageWMS.prototype.getImageInternal = function(extent, resolution, pix
   };
   ol.obj.assign(params, this.params_);
 
-  this.imageSize_[0] = imageWidth * this.ratio_;
-  this.imageSize_[1] = imageHeight * this.ratio_;
+  this.imageSize_[0] = Math.round(ol.extent.getWidth(requestExtent) / imageResolution);
+  this.imageSize_[1] = Math.round(ol.extent.getHeight(requestExtent) / imageResolution);
 
-  var url = this.getRequestUrl_(extent, this.imageSize_, pixelRatio,
+  var url = this.getRequestUrl_(requestExtent, this.imageSize_, pixelRatio,
       projection, params);
 
-  this.image_ = new ol.Image(extent, resolution, pixelRatio,
+  this.image_ = new ol.Image(requestExtent, resolution, pixelRatio,
       this.getAttributions(), url, this.crossOrigin_, this.imageLoadFunction_);
 
   this.renderedRevision_ = this.getRevision();
diff --git a/test/spec/ol/source/imagewms.test.js b/test/spec/ol/source/imagewms.test.js
index 84aaa30205..3e6ca560fb 100644
--- a/test/spec/ol/source/imagewms.test.js
+++ b/test/spec/ol/source/imagewms.test.js
@@ -24,6 +24,30 @@ describe('ol.source.ImageWMS', function() {
   describe('#getImage', function() {
 
     it('returns the expected image URL', function() {
+      options.ratio = 1.5;
+      var source = new ol.source.ImageWMS(options);
+      var image = source.getImage([10, 20, 30.1, 39.9], resolution, pixelRatio, projection);
+      var uri = new URL(image.src_);
+      var queryData = uri.searchParams;
+      var extent = queryData.get('BBOX').split(',').map(Number);
+      var extentAspectRatio = (extent[3] - extent[1]) / (extent[2] - extent[0]);
+      var imageAspectRatio = Number(queryData.get('WIDTH') / Number(queryData.get('HEIGHT')));
+      expect(extentAspectRatio).to.roughlyEqual(imageAspectRatio, 1e-12);
+    });
+
+    it('requests integer WIDTH and HEIGHT', function() {
+      options.ratio = 1.5;
+      var source = new ol.source.ImageWMS(options);
+      var image = source.getImage([10, 20, 30.1, 39.9], resolution, pixelRatio, projection);
+      var uri = new URL(image.src_);
+      var queryData = uri.searchParams;
+      var width = parseFloat(queryData.get('WIDTH'));
+      var height = parseFloat(queryData.get('HEIGHT'));
+      expect(width).to.be(Math.round(width));
+      expect(height).to.be(Math.round(height));
+    });
+
+    it('sets WIDTH and HEIGHT to match the aspect ratio of BBOX', function() {
       var source = new ol.source.ImageWMS(options);
       var image = source.getImage(extent, resolution, pixelRatio, projection);
       var uri = new URL(image.src_);