diff --git a/src/wp-admin/includes/comment.php b/src/wp-admin/includes/comment.php
index dfb39220ab..32cb56b5fb 100644
--- a/src/wp-admin/includes/comment.php
+++ b/src/wp-admin/includes/comment.php
@@ -9,19 +9,30 @@
 /**
  * Determine if a comment exists based on author and date.
  *
+ * For best performance, use `$timezone = 'gmt'`, which queries a field that is properly indexed. The default value
+ * for `$timezone` is 'blog' for legacy reasons.
+ *
  * @since 2.0.0
+ * @since 4.4.0 Added the `$timezone` parameter.
  *
  * @global wpdb $wpdb WordPress database abstraction object.
  *
- * @param string $comment_author Author of the comment
- * @param string $comment_date Date of the comment
+ * @param string $comment_author Author of the comment.
+ * @param string $comment_date   Date of the comment.
+ * @param string $timezone       Timezone. Accepts 'blog' or 'gmt'. Default 'blog'.
+ *
  * @return mixed Comment post ID on success.
  */
-function comment_exists($comment_author, $comment_date) {
+function comment_exists( $comment_author, $comment_date, $timezone = 'blog' ) {
 	global $wpdb;
 
+	$date_field = 'comment_date';
+	if ( 'gmt' === $timezone ) {
+		$date_field = 'comment_date_gmt';
+	}
+
 	return $wpdb->get_var( $wpdb->prepare("SELECT comment_post_ID FROM $wpdb->comments
-			WHERE comment_author = %s AND comment_date = %s",
+			WHERE comment_author = %s AND $date_field = %s",
 			stripslashes( $comment_author ),
 			stripslashes( $comment_date )
 	) );
diff --git a/tests/phpunit/tests/admin/includesComment.php b/tests/phpunit/tests/admin/includesComment.php
index 5b7b01b904..fe9b86cb72 100644
--- a/tests/phpunit/tests/admin/includesComment.php
+++ b/tests/phpunit/tests/admin/includesComment.php
@@ -23,4 +23,64 @@ class Tests_Admin_IncludesComment extends WP_UnitTestCase {
 		$this->assertNull( comment_exists( 1, '2004-01-02 12:00:00' ) );
 		$this->assertEquals( $p1, comment_exists( 1, '2014-05-06 12:00:00' ) );
 	}
+
+	/**
+	 * @ticket 33871
+	 */
+	public function test_default_value_of_timezone_should_be_blog() {
+		$p = $this->factory->post->create();
+		$c = $this->factory->comment->create( array(
+			'comment_author' => 1,
+			'comment_post_ID' => $p,
+			'comment_date' => '2014-05-06 12:00:00',
+			'comment_date_gmt' => '2014-05-06 07:00:00',
+		) );
+
+		$this->assertEquals( $p, comment_exists( 1, '2014-05-06 12:00:00' ) );
+	}
+
+	/**
+	 * @ticket 33871
+	 */
+	public function test_should_respect_timezone_blog() {
+		$p = $this->factory->post->create();
+		$c = $this->factory->comment->create( array(
+			'comment_author' => 1,
+			'comment_post_ID' => $p,
+			'comment_date' => '2014-05-06 12:00:00',
+			'comment_date_gmt' => '2014-05-06 07:00:00',
+		) );
+
+		$this->assertEquals( $p, comment_exists( 1, '2014-05-06 12:00:00', 'blog' ) );
+	}
+
+	/**
+	 * @ticket 33871
+	 */
+	public function test_should_respect_timezone_gmt() {
+		$p = $this->factory->post->create();
+		$c = $this->factory->comment->create( array(
+			'comment_author' => 1,
+			'comment_post_ID' => $p,
+			'comment_date' => '2014-05-06 12:00:00',
+			'comment_date_gmt' => '2014-05-06 07:00:00',
+		) );
+
+		$this->assertEquals( $p, comment_exists( 1, '2014-05-06 07:00:00', 'gmt' ) );
+	}
+
+	/**
+	 * @ticket 33871
+	 */
+	public function test_invalid_timezone_should_fall_back_on_blog() {
+		$p = $this->factory->post->create();
+		$c = $this->factory->comment->create( array(
+			'comment_author' => 1,
+			'comment_post_ID' => $p,
+			'comment_date' => '2014-05-06 12:00:00',
+			'comment_date_gmt' => '2014-05-06 07:00:00',
+		) );
+
+		$this->assertEquals( $p, comment_exists( 1, '2014-05-06 12:00:00', 'not_a_valid_value' ) );
+	}
 }