diff --git a/src/wp-includes/class-walker-comment.php b/src/wp-includes/class-walker-comment.php
index 9df2d20b3bfc5..970caf6060047 100644
--- a/src/wp-includes/class-walker-comment.php
+++ b/src/wp-includes/class-walker-comment.php
@@ -310,7 +310,7 @@ protected function comment( $comment, $depth, $args ) {
 		<?php endif; ?>
 		<div class="comment-author vcard">
 			<?php
-			if ( 0 != $args['avatar_size'] ) {
+			if ( 0 !== (int) $args['avatar_size'] ) {
 				echo get_avatar( $comment, $args['avatar_size'] );
 			}
 			?>
@@ -413,7 +413,7 @@ protected function html5_comment( $comment, $depth, $args ) {
 				<footer class="comment-meta">
 					<div class="comment-author vcard">
 						<?php
-						if ( 0 != $args['avatar_size'] ) {
+						if ( 0 !== (int) $args['avatar_size'] ) {
 							echo get_avatar( $comment, $args['avatar_size'] );
 						}
 						?>
diff --git a/tests/phpunit/tests/comment/walker.php b/tests/phpunit/tests/comment/walker.php
index 27fea21b18d58..473a68c6d0832 100644
--- a/tests/phpunit/tests/comment/walker.php
+++ b/tests/phpunit/tests/comment/walker.php
@@ -45,6 +45,20 @@ function test_has_children() {
 			array( $comment_child, $comment_parent )
 		);
 	}
+
+	public function test_do_not_output_avatar_size_on_empty_string() {
+		$comment_id = self::factory()->comment->create( array( 'comment_post_ID' => $this->post_id ) );
+		$comment    = get_comment( $comment_id );
+		$output     = wp_list_comments(
+			array(
+				'walker'      => new Walker_Comment(),
+				'echo'        => false,
+				'avatar_size' => '',
+			),
+			array( $comment )
+		);
+		$this->assertNotContains( 'gravatar.com/avatar', $output );
+	}
 }
 
 class Comment_Callback_Test {