diff --git a/src/wp-includes/taxonomy.php b/src/wp-includes/taxonomy.php
index 16bdf26ae8..ccaae9041b 100644
--- a/src/wp-includes/taxonomy.php
+++ b/src/wp-includes/taxonomy.php
@@ -3783,7 +3783,7 @@ function update_object_term_cache($object_ids, $object_type) {
 
 	$object_terms = array();
 	foreach ( (array) $terms as $term )
-		$object_terms[$term->object_id][$term->taxonomy][$term->term_id] = $term;
+		$object_terms[$term->object_id][$term->taxonomy][] = $term;
 
 	foreach ( $ids as $id ) {
 		foreach ( $taxonomies as $taxonomy ) {
diff --git a/tests/phpunit/tests/term.php b/tests/phpunit/tests/term.php
index 78f4d29dc0..588b1dc9c8 100644
--- a/tests/phpunit/tests/term.php
+++ b/tests/phpunit/tests/term.php
@@ -1584,6 +1584,35 @@ class Tests_Term extends WP_UnitTestCase {
 		$this->assertEquals( 'This description is even more amazing!', $terms[0]->description );
 	}
 
+	/**
+	 * @ticket 31086
+	 */
+	public function test_get_the_terms_should_return_zero_indexed_array_when_cache_is_empty() {
+		register_taxonomy( 'wptests_tax', 'post' );
+		$p = $this->factory->post->create();
+		wp_set_object_terms( $p, array( 'foo', 'bar' ), 'wptests_tax' );
+
+		$found = get_the_terms( $p, 'wptests_tax' );
+
+		$this->assertEqualSets( array( 0, 1 ), array_keys( $found ) );
+	}
+
+	/**
+	 * @ticket 31086
+	 */
+	public function test_get_the_terms_should_return_zero_indexed_array_when_cache_is_primed() {
+		register_taxonomy( 'wptests_tax', 'post' );
+		$p = $this->factory->post->create();
+		wp_set_object_terms( $p, array( 'foo', 'bar' ), 'wptests_tax' );
+
+		// Prime cache.
+		update_object_term_cache( array( $p ), array( 'post' ) );
+
+		$found = get_the_terms( $p, 'wptests_tax' );
+
+		$this->assertEqualSets( array( 0, 1 ), array_keys( $found ) );
+	}
+
 	/**
 	 * @ticket 19205
 	 */