diff --git a/src/wp-includes/taxonomy.php b/src/wp-includes/taxonomy.php
index 2eecfecf7c..b8261dfeec 100644
--- a/src/wp-includes/taxonomy.php
+++ b/src/wp-includes/taxonomy.php
@@ -832,7 +832,7 @@ class WP_Tax_Query {
 	 * @return bool  Whether the query clause is a first-order clause.
 	 */
 	protected static function is_first_order_clause( $query ) {
-		return empty( $query ) || array_key_exists( 'terms', $query ) || array_key_exists( 'taxonomy', $query ) || array_key_exists( 'include_children', $query ) || array_key_exists( 'field', $query ) || array_key_exists( 'operator', $query );
+		return is_array( $query ) && ( empty( $query ) || array_key_exists( 'terms', $query ) || array_key_exists( 'taxonomy', $query ) || array_key_exists( 'include_children', $query ) || array_key_exists( 'field', $query ) || array_key_exists( 'operator', $query ) );
 	}
 
 	/**
diff --git a/tests/phpunit/tests/term/query.php b/tests/phpunit/tests/term/query.php
index 57dac3610c..17786fea7c 100644
--- a/tests/phpunit/tests/term/query.php
+++ b/tests/phpunit/tests/term/query.php
@@ -85,6 +85,21 @@ class Tests_Tax_Query extends WP_UnitTestCase {
 		$this->assertEquals( array( 'foo', ), $tq->queries[0]['terms'] );
 	}
 
+	/**
+	 * @ticket 30117
+	 */
+	public function test_construct_empty_strings_array_members_should_be_discarded() {
+		$q = new WP_Tax_Query( array(
+			'',
+			array(
+				'taxonomy' => 'post_tag',
+				'terms' => 'foo',
+			),
+		) );
+
+		$this->assertSame( 1, count( $q->queries ) );
+	}
+
 	public function test_transform_query_terms_empty() {
 		$tq = new WP_Tax_Query( array(
 			array(),