diff --git a/src/wp-includes/link-template.php b/src/wp-includes/link-template.php
index 0e746becb0..be39e36279 100644
--- a/src/wp-includes/link-template.php
+++ b/src/wp-includes/link-template.php
@@ -1687,6 +1687,18 @@ function get_adjacent_post( $in_same_term = false, $excluded_terms = '', $previo
 	$where    = '';
 	$adjacent = $previous ? 'previous' : 'next';
 
+	if ( ! empty( $excluded_terms ) && ! is_array( $excluded_terms ) ) {
+		// back-compat, $excluded_terms used to be $excluded_terms with IDs separated by " and "
+		if ( false !== strpos( $excluded_terms, ' and ' ) ) {
+			_deprecated_argument( __FUNCTION__, '3.3.0', sprintf( __( 'Use commas instead of %s to separate excluded terms.' ), "'and'" ) );
+			$excluded_terms = explode( ' and ', $excluded_terms );
+		} else {
+			$excluded_terms = explode( ',', $excluded_terms );
+		}
+
+		$excluded_terms = array_map( 'intval', $excluded_terms );
+	}
+
 	/**
 	 * Filters the IDs of terms excluded from adjacent post queries.
 	 *
@@ -1695,23 +1707,11 @@ function get_adjacent_post( $in_same_term = false, $excluded_terms = '', $previo
 	 *
 	 * @since 4.4.0
 	 *
-	 * @param string $excluded_terms Array of excluded term IDs.
+	 * @param array $excluded_terms Array of excluded term IDs.
 	 */
 	$excluded_terms = apply_filters( "get_{$adjacent}_post_excluded_terms", $excluded_terms );
 
 	if ( $in_same_term || ! empty( $excluded_terms ) ) {
-		if ( ! empty( $excluded_terms ) && ! is_array( $excluded_terms ) ) {
-			// back-compat, $excluded_terms used to be $excluded_terms with IDs separated by " and "
-			if ( false !== strpos( $excluded_terms, ' and ' ) ) {
-				_deprecated_argument( __FUNCTION__, '3.3.0', sprintf( __( 'Use commas instead of %s to separate excluded terms.' ), "'and'" ) );
-				$excluded_terms = explode( ' and ', $excluded_terms );
-			} else {
-				$excluded_terms = explode( ',', $excluded_terms );
-			}
-
-			$excluded_terms = array_map( 'intval', $excluded_terms );
-		}
-
 		if ( $in_same_term ) {
 			$join  .= " INNER JOIN $wpdb->term_relationships AS tr ON p.ID = tr.object_id INNER JOIN $wpdb->term_taxonomy tt ON tr.term_taxonomy_id = tt.term_taxonomy_id";
 			$where .= $wpdb->prepare( 'AND tt.taxonomy = %s', $taxonomy );
diff --git a/tests/phpunit/tests/link/getAdjacentPost.php b/tests/phpunit/tests/link/getAdjacentPost.php
index 83ff42c3fc..649d1547f4 100644
--- a/tests/phpunit/tests/link/getAdjacentPost.php
+++ b/tests/phpunit/tests/link/getAdjacentPost.php
@@ -312,6 +312,40 @@ class Tests_Link_GetAdjacentPost extends WP_UnitTestCase {
 		$this->assertSame( $p3, $found->ID );
 	}
 
+	/**
+	 * @ticket 43521
+	 */
+	public function test_excluded_terms_filter_empty() {
+		register_taxonomy( 'wptests_tax', 'post' );
+
+		$terms = self::factory()->term->create_many(
+			2,
+			array(
+				'taxonomy' => 'wptests_tax',
+			)
+		);
+
+		$p1 = self::factory()->post->create( array( 'post_date' => '2015-08-27 12:00:00' ) );
+		$p2 = self::factory()->post->create( array( 'post_date' => '2015-08-26 12:00:00' ) );
+		$p3 = self::factory()->post->create( array( 'post_date' => '2015-08-25 12:00:00' ) );
+
+		wp_set_post_terms( $p1, array( $terms[0], $terms[1] ), 'wptests_tax' );
+		wp_set_post_terms( $p2, array( $terms[1] ), 'wptests_tax' );
+		wp_set_post_terms( $p3, array( $terms[0] ), 'wptests_tax' );
+
+		$this->go_to( get_permalink( $p1 ) );
+
+		$this->exclude_term = $terms[1];
+		add_filter( 'get_previous_post_excluded_terms', array( $this, 'filter_excluded_terms' ) );
+
+		$found = get_adjacent_post( false, array(), true, 'wptests_tax' );
+
+		remove_filter( 'get_previous_post_excluded_terms', array( $this, 'filter_excluded_terms' ) );
+		unset( $this->exclude_term );
+
+		$this->assertSame( $p3, $found->ID );
+	}
+
 	public function filter_excluded_terms( $excluded_terms ) {
 		$excluded_terms[] = $this->exclude_term;
 		return $excluded_terms;