diff --git src/wp-includes/link-template.php src/wp-includes/link-template.php
index 9a27404..365b14b 100644
--- src/wp-includes/link-template.php
+++ src/wp-includes/link-template.php
@@ -1682,6 +1682,18 @@ function get_adjacent_post( $in_same_term = false, $excluded_terms = '', $previo
 	$where    = '';
 	$adjacent = $previous ? 'previous' : 'next';
 
+	/**
+	 * Filters the IDs of terms excluded from adjacent post queries.
+	 *
+	 * The dynamic portion of the hook name, `$adjacent`, refers to the type
+	 * of adjacency, 'next' or 'previous'.
+	 *
+	 * @since 4.4.0
+	 *
+	 * @param string $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 "
@@ -1715,18 +1727,6 @@ function get_adjacent_post( $in_same_term = false, $excluded_terms = '', $previo
 			$where .= ' AND tt.term_id IN (' . implode( ',', $term_array ) . ')';
 		}
 
-		/**
-		 * Filters the IDs of terms excluded from adjacent post queries.
-		 *
-		 * The dynamic portion of the hook name, `$adjacent`, refers to the type
-		 * of adjacency, 'next' or 'previous'.
-		 *
-		 * @since 4.4.0
-		 *
-		 * @param string $excluded_terms Array of excluded term IDs.
-		 */
-		$excluded_terms = apply_filters( "get_{$adjacent}_post_excluded_terms", $excluded_terms );
-
 		if ( ! empty( $excluded_terms ) ) {
 			$where .= " AND p.ID NOT IN ( SELECT tr.object_id FROM $wpdb->term_relationships tr LEFT JOIN $wpdb->term_taxonomy tt ON (tr.term_taxonomy_id = tt.term_taxonomy_id) WHERE tt.term_id IN (" . implode( ',', array_map( 'intval', $excluded_terms ) ) . ') )';
 		}
diff --git tests/phpunit/tests/link/getAdjacentPost.php tests/phpunit/tests/link/getAdjacentPost.php
index 0c38e63..07bdc4d 100644
--- tests/phpunit/tests/link/getAdjacentPost.php
+++ tests/phpunit/tests/link/getAdjacentPost.php
@@ -276,6 +276,39 @@ 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;