Index: class-wp-image-editor-gd.php
===================================================================
--- class-wp-image-editor-gd.php	(revision 27100)
+++ class-wp-image-editor-gd.php	(working copy)
@@ -205,12 +205,22 @@
 		$orig_size = $this->size;
 
 		foreach ( $sizes as $size => $size_data ) {
-			if ( ! ( isset( $size_data['width'] ) && isset( $size_data['height'] ) ) )
+			if ( ! isset( $size_data['width'] ) && ! isset( $size_data['height'] ) )
 				continue;
 
+			if ( ! isset( $size_data['width'] ) )
+				$size_data['width'] = 0;
+			if ( ! isset( $size_data['height'] ) )
+				$size_data['height'] = 0;
+
 			if ( ! isset( $size_data['crop'] ) )
 				$size_data['crop'] = false;
+			if ( ! isset( $size_data['crop'] ) )
+				$size_data['crop'] = false;
 
+			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 ) ) {