diff --git a/src/wp-includes/media.php b/src/wp-includes/media.php
index 89e642bd3b..b71c0b4d72 100644
--- a/src/wp-includes/media.php
+++ b/src/wp-includes/media.php
@@ -190,6 +190,20 @@ function add_image_size( $name, $width = 0, $height = 0, $crop = false ) {
 	$_wp_additional_image_sizes[$name] = array( 'width' => absint( $width ), 'height' => absint( $height ), 'crop' => (bool) $crop );
 }
 
+/**
+ * Check if an image size exists
+ *
+ * @since 3.9.0
+ *
+ * @param string $name The image size name.
+ * @return bool True if it exists, false if not.
+ */
+function has_image_size( $name = '' ) {
+	global $_wp_additional_image_sizes;
+
+	return isset( $_wp_additional_image_sizes[$name] );
+}
+
 /**
  * Registers an image size for the post thumbnail
  *