diff --git a/src/wp-admin/includes/upgrade.php b/src/wp-admin/includes/upgrade.php
index 330cfad8e9..b1c4bc28fa 100644
--- a/src/wp-admin/includes/upgrade.php
+++ b/src/wp-admin/includes/upgrade.php
@@ -1980,12 +1980,23 @@ function dbDelta( $queries = '', $execute = true ) {
 						$index_columns .= '('.$column_data['subpart'].')';
 					}
 				}
+
+				// The alternative index string doesn't care about subparts
+				$alt_index_columns = preg_replace( '/\([^)]*\)/', '', $index_columns );
+
 				// Add the column list to the index create string.
-				$index_string .= ' ('.$index_columns.')';
-				if (!(($aindex = array_search($index_string, $indices)) === false)) {
-					unset($indices[$aindex]);
-					// todo: Remove this?
-					//echo "<pre style=\"border:1px solid #ccc;margin-top:5px;\">{$table}:<br />Found index:".$index_string."</pre>\n";
+				$index_strings = array(
+					"$index_string ($index_columns)",
+					"$index_string ($alt_index_columns)",
+				);
+
+				foreach( $index_strings as $index_string ) {
+					if ( ! ( ( $aindex = array_search( $index_string, $indices ) ) === false ) ) {
+						unset( $indices[ $aindex ] );
+						break;
+						// todo: Remove this?
+						//echo "<pre style=\"border:1px solid #ccc;margin-top:5px;\">{$table}:<br />Found index:".$index_string."</pre>\n";
+					}
 				}
 				// todo: Remove this?
 				//else echo "<pre style=\"border:1px solid #ccc;margin-top:5px;\">{$table}:<br /><b>Did not find index:</b>".$index_string."<br />".print_r($indices, true)."</pre>\n";
diff --git a/tests/phpunit/tests/dbdelta.php b/tests/phpunit/tests/dbdelta.php
new file mode 100755
index 0000000000..6cdc325dab
--- /dev/null
+++ b/tests/phpunit/tests/dbdelta.php
@@ -0,0 +1,43 @@
+<?php
+
+/**
+ * Test dbDelta()
+ *
+ * @group upgrade
+ * @group dbdelta
+ */
+class Tests_dbDelta extends WP_UnitTestCase {
+
+	function test_create_new_table() {
+		include_once( ABSPATH . 'wp-admin/includes/upgrade.php');
+		$table_name = 'test_new_table';
+
+		$create = "CREATE TABLE $table_name (\n a varchar(255)\n)";
+		$expected = array( $table_name => "Created table $table_name" );
+
+		$actual = dbDelta( $create, false );
+
+		$this->assertSame( $expected, $actual );
+	}
+
+	/**
+	 * @ticket 31869
+	 */
+	function test_truncated_index() {
+		global $wpdb;
+
+		if ( ! $wpdb->has_cap( 'utf8mb4' ) ) {
+			$this->markTestSkipped( 'This test requires utf8mb4 support in MySQL.' );
+		}
+
+		include_once( ABSPATH . 'wp-admin/includes/upgrade.php');
+		$table_name = 'test_truncated_index';
+
+		$create = "CREATE TABLE $table_name (\n a varchar(255) COLLATE utf8mb4_unicode_ci,\n KEY a (a)\n)";
+		$wpdb->query( $create );
+
+		$actual = dbDelta( $create, false );
+
+		$this->assertSame( array(), $actual );
+	}
+}