diff --git a/src/wp-admin/includes/class-custom-image-header.php b/src/wp-admin/includes/class-custom-image-header.php
index c8809ade2f..12ac1ef9e2 100644
--- a/src/wp-admin/includes/class-custom-image-header.php
+++ b/src/wp-admin/includes/class-custom-image-header.php
@@ -332,7 +332,7 @@ class Custom_Image_Header {
 			if ( ! empty( $header['attachment_id'] ) ) {
 				$width = ' width="230"';
 			}
-			echo '<img src="' . set_url_scheme( $header_thumbnail ) . '" alt="' . esc_attr( $header_alt_text ) . '"' . $width . ' /></label>';
+			echo '<img src="' . esc_url( set_url_scheme( $header_thumbnail ) ) . '" alt="' . esc_attr( $header_alt_text ) . '"' . $width . ' /></label>';
 			echo '</div>';
 		}