diff --git a/wp-thumbor.php b/wp-thumbor.php
index e0a02ac..8900077 100644
--- a/wp-thumbor.php
+++ b/wp-thumbor.php
@@ -298,7 +298,15 @@ function wp_thumbor_output_buffer_callback($buffer) {
             foreach ( $srcsetItems as $item ) {
                 $parts = preg_split('/\s+/', trim($item));
                 if ( ! empty($parts[0]) && preg_match('/^https?:\/\//', $parts[0]) ) {
-                    $newURL = wp_thumbor_transform_url($parts[0]);
+		    $width  = null;
+		    $height = null;
+		    if ( isset($parts[1]) && preg_match('/^(\d+)w$/i', $parts[1], $m) ) {
+		        $width = intval($m[1]);
+		    } elseif ( isset($parts[1]) && preg_match('/^(\d+)h$/i', $parts[1], $m) ) {
+		        $height = intval($m[1]);
+		    }
+		    $newURL = wp_thumbor_transform_url($parts[0], $width, $height);
+
                     $newSrcset[] = isset($parts[1]) ? $newURL . ' ' . $parts[1] : $newURL;
                 } else {
                     $newSrcset[] = $item;