diff --git a/src/wp-includes/class-wp-comment-query.php b/src/wp-includes/class-wp-comment-query.php
index 0920ca229f..825e9d882b 100644
--- a/src/wp-includes/class-wp-comment-query.php
+++ b/src/wp-includes/class-wp-comment-query.php
@@ -995,8 +995,16 @@ class WP_Comment_Query {
 			}
 
 			if ( $uncached_parent_ids ) {
-				$where = 'WHERE ' . $_where . ' AND comment_parent IN (' . implode( ',', array_map( 'intval', $uncached_parent_ids ) ) . ')';
-				$level_comments = $wpdb->get_results( "SELECT $wpdb->comments.comment_ID, $wpdb->comments.comment_parent {$this->sql_clauses['from']} {$where} {$this->sql_clauses['groupby']} ORDER BY comment_date_gmt ASC, comment_ID ASC" );
+				// Fetch this level of comments.
+				$parent_query_args = $this->query_vars;
+				foreach ( $exclude_keys as $exclude_key ) {
+					$parent_query_args[ $exclude_key ] = '';
+				}
+				$parent_query_args['parent__in']    = $uncached_parent_ids;
+				$parent_query_args['no_found_rows'] = true;
+				$parent_query_args['hierarchical']  = false;
+
+				$level_comments = get_comments( $parent_query_args );
 
 				// Cache parent-child relationships.
 				$parent_map = array_fill_keys( $uncached_parent_ids, array() );
diff --git a/tests/phpunit/tests/comment/query.php b/tests/phpunit/tests/comment/query.php
index 219e2d1933..1c4544bd0b 100644
--- a/tests/phpunit/tests/comment/query.php
+++ b/tests/phpunit/tests/comment/query.php
@@ -2498,6 +2498,55 @@ class Tests_Comment_Query extends WP_UnitTestCase {
 		$this->assertSame( $num_queries, $wpdb->num_queries );
 	}
 
+	/**
+	 * @ticket 37696
+	 */
+	public function test_hierarchy_should_be_filled_when_cache_is_incomplete() {
+		global $wpdb;
+
+		$p = self::factory()->post->create();
+		$comment_1 = self::factory()->comment->create( array(
+			'comment_post_ID' => $p,
+			'comment_approved' => '1',
+		) );
+		$comment_2 = self::factory()->comment->create( array(
+			'comment_post_ID' => $p,
+			'comment_approved' => '1',
+			'comment_parent' => $comment_1,
+		) );
+		$comment_3 = self::factory()->comment->create( array(
+			'comment_post_ID' => $p,
+			'comment_approved' => '1',
+			'comment_parent' => $comment_1,
+		) );
+		$comment_4 = self::factory()->comment->create( array(
+			'comment_post_ID' => $p,
+			'comment_approved' => '1',
+			'comment_parent' => $comment_2,
+		) );
+
+		// Prime cache.
+		$q1 = new WP_Comment_Query( array(
+			'post_id' => $p,
+			'hierarchical' => true,
+		) );
+		$q1_ids = wp_list_pluck( $q1->comments, 'comment_ID' );
+		$this->assertEqualSets( array( $comment_1, $comment_2, $comment_3, $comment_4 ), $q1_ids );
+
+		// Delete one of the parent caches.
+		$last_changed = wp_cache_get( 'last_changed', 'comment' );
+		$key = md5( serialize( wp_array_slice_assoc( $q1->query_vars, array_keys( $q1->query_var_defaults ) ) ) );
+		$cache_key = "get_comment_child_ids:$comment_2:$key:$last_changed";
+		wp_cache_delete( $cache_key, 'comment' );
+
+		$q2 = new WP_Comment_Query( array(
+			'post_id' => $p,
+			'hierarchical' => true,
+		) );
+		$q2_ids = wp_list_pluck( $q2->comments, 'comment_ID' );
+		$this->assertEqualSets( $q1_ids, $q2_ids );
+	}
+
 	/**
 	 * @ticket 27571
 	 */