diff --git wp-includes/class-wp-image-editor-gd.php wp-includes/class-wp-image-editor-gd.php
index 050e696..bb69b62 100644
--- wp-includes/class-wp-image-editor-gd.php
+++ wp-includes/class-wp-image-editor-gd.php
@@ -173,10 +173,13 @@ class WP_Image_Editor_GD extends WP_Image_Editor {
 	 * Processes current image and saves to disk
 	 * multiple sizes from single source.
 	 *
+	 * 'width' and 'height' are required.
+	 * 'crop' defaults to false when not provided.
+	 *
 	 * @since 3.5.0
 	 * @access public
 	 *
-	 * @param array $sizes { {'width'=>int, 'height'=>int, 'crop'=>bool}, ... }
+	 * @param array $sizes { {'width'=>int, 'height'=>int, ['crop'=>bool]}, ... }
 	 * @return array
 	 */
 	public function multi_resize( $sizes ) {
@@ -184,6 +187,12 @@ class WP_Image_Editor_GD extends WP_Image_Editor {
 		$orig_size = $this->size;
 
 		foreach ( $sizes as $size => $size_data ) {
+			if ( ! ( isset( $size_data['width'] ) && isset( $size_data['height'] ) ) )
+				continue;
+
+			if ( ! isset( $size_data['crop'] ) )
+				$size_data['crop'] = false;
+
 			$image = $this->_resize( $size_data['width'], $size_data['height'], $size_data['crop'] );
 
 			if( ! is_wp_error( $image ) ) {
diff --git wp-includes/class-wp-image-editor-imagick.php wp-includes/class-wp-image-editor-imagick.php
index 457b7fc..653eb8a 100644
--- wp-includes/class-wp-image-editor-imagick.php
+++ wp-includes/class-wp-image-editor-imagick.php
@@ -245,10 +245,13 @@ class WP_Image_Editor_Imagick extends WP_Image_Editor {
 	 * Processes current image and saves to disk
 	 * multiple sizes from single source.
 	 *
+	 * 'width' and 'height' are required.
+	 * 'crop' defaults to false when not provided.
+	 *
 	 * @since 3.5.0
 	 * @access public
 	 *
-	 * @param array $sizes { {'width'=>int, 'height'=>int, 'crop'=>bool}, ... }
+	 * @param array $sizes { {'width'=>int, 'height'=>int, ['crop'=>bool]}, ... }
 	 * @return array
 	 */
 	public function multi_resize( $sizes ) {
@@ -260,6 +263,12 @@ class WP_Image_Editor_Imagick extends WP_Image_Editor {
 			if ( ! $this->image )
 				$this->image = $orig_image->getImage();
 
+			if ( ! ( isset( $size_data['width'] ) && isset( $size_data['height'] ) ) )
+				continue;
+
+			if ( ! isset( $size_data['crop'] ) )
+				$size_data['crop'] = false;
+
 			$resize_result = $this->resize( $size_data['width'], $size_data['height'], $size_data['crop'] );
 
 			if( ! is_wp_error( $resize_result ) ) {
diff --git wp-includes/class-wp-image-editor.php wp-includes/class-wp-image-editor.php
index 1125602..1d7b80e 100644
--- wp-includes/class-wp-image-editor.php
+++ wp-includes/class-wp-image-editor.php
@@ -97,11 +97,14 @@ abstract class WP_Image_Editor {
 	 * Processes current image and saves to disk
 	 * multiple sizes from single source.
 	 *
+	 * 'width' and 'height' are required.
+	 * 'crop' defaults to false when not provided.
+	 *
 	 * @since 3.5.0
 	 * @access public
 	 * @abstract
 	 *
-	 * @param array $sizes { {'width'=>int, 'height'=>int, 'crop'=>bool}, ... }
+	 * @param array $sizes { {'width'=>int, 'height'=>int, ['crop'=>bool]}, ... }
 	 * @return array
 	 */
 	abstract public function multi_resize( $sizes );