diff --git a/wp-includes/pluggable.php b/wp-includes/pluggable.php
index 5fed477bce..52a16788fc 100644
--- a/wp-includes/pluggable.php
+++ b/wp-includes/pluggable.php
@@ -2173,7 +2173,8 @@ function get_avatar( $id_or_email, $size = '96', $default = '', $alt = false ) {
 		$out = str_replace( '&', '&', esc_url( $out ) );
 		$avatar = "<img alt='{$safe_alt}' src='{$out}' class='avatar avatar-{$size} photo' height='{$size}' width='{$size}' />";
 	} else {
-		$avatar = "<img alt='{$safe_alt}' src='{$default}' class='avatar avatar-{$size} photo avatar-default' height='{$size}' width='{$size}' />";
+		$out = esc_url( $default );
+		$avatar = "<img alt='{$safe_alt}' src='{$out}' class='avatar avatar-{$size} photo avatar-default' height='{$size}' width='{$size}' />";
 	}
 
 	/**