diff --git a/src/wp-includes/taxonomy.php b/src/wp-includes/taxonomy.php
index 9a3a13cb29..1c63b9be03 100644
--- a/src/wp-includes/taxonomy.php
+++ b/src/wp-includes/taxonomy.php
@@ -2063,7 +2063,7 @@ function wp_insert_term( $term, $taxonomy, $args = array() ) {
 				$siblings = get_terms( $taxonomy, array( 'get' => 'all', 'parent' => $parent ) );
 
 				$existing_term = null;
-				if ( $name_match->slug === $slug && in_array( $name, wp_list_pluck( $siblings, 'name' ) ) ) {
+				if ( ( ! $slug_provided || $name_match->slug === $slug ) && in_array( $name, wp_list_pluck( $siblings, 'name' ) ) ) {
 					$existing_term = $name_match;
 				} elseif ( $slug_match && in_array( $slug, wp_list_pluck( $siblings, 'slug' ) ) ) {
 					$existing_term = $slug_match;
diff --git a/tests/phpunit/tests/term/wpInsertTerm.php b/tests/phpunit/tests/term/wpInsertTerm.php
index 6ec7ee9864..21b6cd79e8 100644
--- a/tests/phpunit/tests/term/wpInsertTerm.php
+++ b/tests/phpunit/tests/term/wpInsertTerm.php
@@ -376,6 +376,23 @@ class Tests_Term_WpInsertTerm extends WP_UnitTestCase {
 		$this->assertSame( 'Foo', $t4_term->name );
 	}
 
+	/**
+	 * @ticket 39984
+	 */
+	public function test_duplicate_name_check_should_fail_when_no_slug_is_provided_even_when_slugs_would_not_clash() {
+		register_taxonomy( 'wptests_tax', 'post', array( 'hierarchical' => true ) );
+		$t1 = self::factory()->term->create( array(
+			'name' => 'Foo',
+			'slug' => 'foo-no-conflict',
+			'taxonomy' => 'wptests_tax',
+		) );
+
+		$error = wp_insert_term( 'Foo', 'wptests_tax' );
+
+		$this->assertWPError( $error );
+		$this->assertSame( 'term_exists', $error->get_error_code() );
+		$this->assertSame( $t1, $error->get_error_data() );
+	}
 	/**
 	 * @ticket 31328
 	 */