Index: src/wp-admin/edit-form-comment.php
===================================================================
--- src/wp-admin/edit-form-comment.php	(revision 33998)
+++ src/wp-admin/edit-form-comment.php	(working copy)
@@ -119,17 +119,19 @@
 <?php
 if ( $comment->comment_parent ) :
 	$parent      = get_comment( $comment->comment_parent );
-	$parent_link = esc_url( get_comment_link( $comment->comment_parent ) );
-	$name        = get_comment_author( $parent->comment_ID );
-?>
-<div class="misc-pub-section misc-pub-reply-to">
-	<?php printf(
-		/* translators: comment link */
-		__( 'In reply to: %s' ),
-		'<b><a href="' . $parent_link . '">' . $name . '</a></b>'
-	); ?>
-</div>
-<?php endif; ?>
+	if ( $parent ) :
+		$parent_link = esc_url( get_comment_link( $comment->comment_parent ) );
+		$name        = get_comment_author( $parent->comment_ID );
+	?>
+	<div class="misc-pub-section misc-pub-reply-to">
+		<?php printf(
+			/* translators: comment link */
+			__( 'In reply to: %s' ),
+			'<b><a href="' . $parent_link . '">' . $name . '</a></b>'
+		); ?>
+	</div>
+<?php endif;
+endif; ?>
 
 <?php
 	/**
Index: src/wp-admin/includes/class-wp-comments-list-table.php
===================================================================
--- src/wp-admin/includes/class-wp-comments-list-table.php	(revision 33998)
+++ src/wp-admin/includes/class-wp-comments-list-table.php	(working copy)
@@ -607,9 +607,11 @@
 
 		if ( $comment->comment_parent ) {
 			$parent = get_comment( $comment->comment_parent );
-			$parent_link = esc_url( get_comment_link( $parent ) );
-			$name = get_comment_author( $parent );
-			printf( ' | '.__( 'In reply to <a href="%1$s">%2$s</a>.' ), $parent_link, $name );
+			if ( $parent ) {
+				$parent_link = esc_url( get_comment_link( $parent ) );
+				$name = get_comment_author( $parent );
+				printf( ' | '.__( 'In reply to <a href="%1$s">%2$s</a>.' ), $parent_link, $name );
+			}
 		}
 
 		echo '</div>';