diff --git a/resources/mmv/ui/mmv.ui.reuse.download.js b/resources/mmv/ui/mmv.ui.reuse.download.js
index b53b90de3..7129efefd 100644
--- a/resources/mmv/ui/mmv.ui.reuse.download.js
+++ b/resources/mmv/ui/mmv.ui.reuse.download.js
@@ -143,34 +143,54 @@
 	 */
 	DP.handleSizeSwitch = function ( item ) {
 		var download = this,
-			value = item.getData(),
-			message = mw.message(
-				'multimediaviewer-download-' + value.name + '-button-name' ).text(),
-			sizeMessage = mw.message( 'multimediaviewer-embed-dimensions-with-file-format',
-				mw.message( 'multimediaviewer-embed-dimensions', value.width, value.height ).text(),
-				this.imageExtension
-			).text();
-
-		// Update button label and size strings to reflect new selected size
-		this.$downloadButton.html(
-			'<span class="multimediaviewer-download-image-size-name">' +
-			message + '</span>' +
-			'<span class="multimediaviewer-download-image-size">' +
-			sizeMessage + '</span>'
-		);
+			value = item.getData();
 
 		// Disable download while we get the image
 		this.$downloadButton.addClass( 'disabledLink' );
+		// Set a temporary message. It will be updated once we have the file type.
+		this.setButtonText( value.name, this.imageExtension, value.width, value.height );
 
 		this.utils.getThumbnailUrlPromise( value.width ).done( function ( thumbnail ) {
 			download.$downloadButton.attr( 'href', thumbnail.url + '?download' );
 			download.$previewLink.attr( 'href', thumbnail.url );
-
+			download.setButtonText( value.name, download.getExtensionFromUrl( thumbnail.url ),
+				value.width, value.height );
 			// Re-enable download
 			download.$downloadButton.removeClass( 'disabledLink' );
 		} );
 	};
 
+	/**
+	 * Sets the text of the download button.
+	 * @param {string} sizeClass A size class such as 'small'
+	 * @param {string} extension file extension
+	 * @param {number} width
+	 * @param {number} height
+	 */
+	DP.setButtonText = function( sizeClass, extension, width, height ) {
+		var sizeClasMessage, sizeMessage, dimensionMessage;
+
+		sizeClasMessage = mw.message( 'multimediaviewer-download-' + sizeClass + '-button-name' ).text();
+		dimensionMessage = mw.message( 'multimediaviewer-embed-dimensions', width, height ).text();
+		sizeMessage = mw.message( 'multimediaviewer-embed-dimensions-with-file-format',
+			dimensionMessage, extension ).text();
+
+		// Update button label and size strings to reflect new selected size
+		this.$downloadButton.html(
+			'<span class="multimediaviewer-download-image-size-name">' + sizeClasMessage + '</span>'
+				+ '<span class="multimediaviewer-download-image-size">' + sizeMessage + '</span>'
+		);
+	};
+
+	/**
+	 * Chops off the extension part of an URL.
+	 * @param {string} url
+	 */
+	DP.getExtensionFromUrl = function( url ) {
+		var urlParts = url.split( '.' );
+		return urlParts[urlParts.length - 1];
+	};
+
 	/**
 	 * Sets the data on the element.
 	 *
diff --git a/tests/qunit/mmv/ui/mmv.ui.reuse.download.test.js b/tests/qunit/mmv/ui/mmv.ui.reuse.download.test.js
index b6682e14b..54a7947f2 100644
--- a/tests/qunit/mmv/ui/mmv.ui.reuse.download.test.js
+++ b/tests/qunit/mmv/ui/mmv.ui.reuse.download.test.js
@@ -16,14 +16,10 @@
  */
 
 ( function ( mw, $ ) {
-	function makeDownload() {
-		return new mw.mmv.ui.reuse.Download( $( '#qunit-fixture' ) );
-	}
-
 	QUnit.module( 'mmv.ui.reuse.download', QUnit.newMwEnvironment() );
 
 	QUnit.test( 'Sanity test, object creation and UI construction', 6, function ( assert ) {
-		var download = makeDownload();
+		var download = new mw.mmv.ui.reuse.Download( $( '#qunit-fixture' ) );
 
 		assert.ok( download, 'download UI element is created.' );
 		assert.strictEqual( download.$pane.length, 1, 'Pane div created.' );
@@ -34,11 +30,11 @@
 	} );
 
 	QUnit.test( 'set()/empty():', 5, function ( assert ) {
-		var download = makeDownload(),
+		var download = new mw.mmv.ui.reuse.Download( $( '#qunit-fixture' ) ),
 			src = 'https://upload.wikimedia.org/wikipedia/commons/3/3a/Foobar.jpg',
 			image = { // fake mw.mmv.model.Image
 				title: new mw.Title( 'File:Foobar.jpg' ),
-				url: src,
+				url: src
 			};
 
 		assert.strictEqual( download.imageExtension, undefined, 'Image extension is not set.' );
@@ -60,10 +56,10 @@
 	} );
 
 	QUnit.test( 'attach()/unattach():', 2, function ( assert ) {
-		var download = makeDownload(),
+		var download = new mw.mmv.ui.reuse.Download( $( '#qunit-fixture' ) ),
 			image = {
 				title: new mw.Title( 'File:Foobar.jpg' ),
-				url: 'https://upload.wikimedia.org/wikipedia/commons/3/3a/Foobar.jpg',
+				url: 'https://upload.wikimedia.org/wikipedia/commons/3/3a/Foobar.jpg'
 			};
 
 		download.set( image );
@@ -111,7 +107,7 @@
 	} );
 
 	QUnit.test( 'handleSizeSwitch():', 6, function ( assert ) {
-		var download = makeDownload(),
+		var download = new mw.mmv.ui.reuse.Download( $( '#qunit-fixture' ) ),
 			newImageUrl = 'https://upload.wikimedia.org/wikipedia/commons/3/3a/NewFoobar.jpg';
 
 		assert.strictEqual( download.$downloadButton.html(), '', 'Button has empty content.' );
@@ -129,4 +125,22 @@
 		assert.strictEqual( download.$previewLink.attr( 'href' ), newImageUrl, 'Preview link href updated.' );
 	} );
 
+	QUnit.test( 'setButtonText() sanity check:', 2, function ( assert ) {
+		var download = new mw.mmv.ui.reuse.Download( $( '#qunit-fixture' ) ),
+			message;
+
+		download.setButtonText( 'large', 'jpg', 100, 200 );
+		assert.ok( true, 'Setting the text did not cause any errors' );
+
+		message = download.$downloadButton.html();
+		download.setButtonText( 'small', 'png', 1000, 2000 );
+		assert.notStrictEqual( download.$downloadButton.html(), message, 'Button text was updated' );
+	} );
+
+	QUnit.test( 'getExtensionFromUrl():', 1, function ( assert ) {
+		var download = new mw.mmv.ui.reuse.Download( $( '#qunit-fixture' ) );
+
+		assert.strictEqual( download.getExtensionFromUrl( 'http://example.com/bing/foo.bar.png' ),
+			'png', 'Extension is parsed correctly' );
+	} );
 }( mediaWiki, jQuery ) );