Index: src/wp-includes/taxonomy-functions.php
===================================================================
--- src/wp-includes/taxonomy-functions.php	(revision 34222)
+++ src/wp-includes/taxonomy-functions.php	(working copy)
@@ -803,7 +803,7 @@
 		$field = 'tt.term_taxonomy_id';
 	} else {
 		$term = get_term( (int) $value, $taxonomy, $output, $filter );
-		if ( is_wp_error( $term ) )
+		if ( is_wp_error( $term ) || is_null( $term ) )
 			$term = false;
 		return $term;
 	}
Index: tests/phpunit/tests/term.php
===================================================================
--- tests/phpunit/tests/term.php	(revision 34044)
+++ tests/phpunit/tests/term.php	(working copy)
@@ -58,6 +58,14 @@
 	}
 
 	/**
+	 * @ticket 33281
+	 */
+	function test_get_term_by_unexisting_id() {
+		$term = get_term_by( 'id', 123456, 'category' );
+		$this->assertFalse( $term );
+	}
+
+	/**
 	 * @ticket 15919
 	 */
 	function test_wp_count_terms() {