diff --git a/lib/classes/text.php b/lib/classes/text.php
index b99b5d6fc6c..7a44b1b807b 100644
--- a/lib/classes/text.php
+++ b/lib/classes/text.php
@@ -248,6 +248,30 @@ class core_text {
         return $result;
     }
 
+    /**
+     * Truncates a string to no more than a certain number of bytes in a multi-byte safe manner.
+     * UTF-8 only!
+     *
+     * Many of the other charsets we test for (like ISO-2022-JP and EUC-JP) are not supported
+     * by typo3, and will give invalid results, so we are supporting UTF-8 only.
+     *
+     * @param string $string String to truncate
+     * @param int $bytes Maximum length of bytes in the result
+     * @return string Portion of string specified by $bytes
+     * @since Moodle 3.1
+     */
+    public static function str_max_bytes($string, $bytes) {
+        if (function_exists('mb_strcut')) {
+            return mb_strcut($string, 0, $bytes, 'UTF-8');
+        }
+
+        $oldlevel = error_reporting(E_PARSE);
+        $result = self::typo3()->strtrunc('utf-8', $string, $bytes);
+        error_reporting($oldlevel);
+
+        return $result;
+    }
+
     /**
      * Finds the last occurrence of a character in a string within another.
      * UTF-8 ONLY safe mb_strrchr().
@@ -707,4 +731,4 @@ class core_text {
         }
         return implode(' ', $words);
     }
-}
\ No newline at end of file
+}
diff --git a/lib/tests/text_test.php b/lib/tests/text_test.php
index 8aeac338431..53e9e57d09c 100644
--- a/lib/tests/text_test.php
+++ b/lib/tests/text_test.php
@@ -179,6 +179,56 @@ class core_text_testcase extends advanced_testcase {
         $this->assertSame(4, core_text::strlen($str, 'GB18030'));
     }
 
+    /**
+     * Test unicode safe string truncation.
+     */
+    public function test_str_max_bytes() {
+        // These are all 3 byte characters, so this is a 12-byte string.
+        $str = '言語設定';
+
+        $this->assertEquals(12, strlen($str));
+
+        // Step back, shortening the string 1 byte at a time. Should remove in 1 char chunks.
+        $conv = core_text::str_max_bytes($str, 12);
+        $this->assertEquals(12, strlen($conv));
+        $this->assertSame('言語設定', $conv);
+        $conv = core_text::str_max_bytes($str, 11);
+        $this->assertEquals(9, strlen($conv));
+        $this->assertSame('言語設', $conv);
+        $conv = core_text::str_max_bytes($str, 10);
+        $this->assertEquals(9, strlen($conv));
+        $this->assertSame('言語設', $conv);
+        $conv = core_text::str_max_bytes($str, 9);
+        $this->assertEquals(9, strlen($conv));
+        $this->assertSame('言語設', $conv);
+        $conv = core_text::str_max_bytes($str, 8);
+        $this->assertEquals(6, strlen($conv));
+        $this->assertSame('言語', $conv);
+
+        // Now try a mixed byte string.
+        $str = '言語設a定';
+
+        $this->assertEquals(13, strlen($str));
+
+        $conv = core_text::str_max_bytes($str, 11);
+        $this->assertEquals(10, strlen($conv));
+        $this->assertSame('言語設a', $conv);
+        $conv = core_text::str_max_bytes($str, 10);
+        $this->assertEquals(10, strlen($conv));
+        $this->assertSame('言語設a', $conv);
+        $conv = core_text::str_max_bytes($str, 9);
+        $this->assertEquals(9, strlen($conv));
+        $this->assertSame('言語設', $conv);
+        $conv = core_text::str_max_bytes($str, 8);
+        $this->assertEquals(6, strlen($conv));
+        $this->assertSame('言語', $conv);
+
+        // Test 0 byte case.
+        $conv = core_text::str_max_bytes($str, 0);
+        $this->assertEquals(0, strlen($conv));
+        $this->assertSame('', $conv);
+    }
+
     /**
      * Tests the static strtolower method.
      */
diff --git a/lib/upgrade.txt b/lib/upgrade.txt
index d23f70200b5..515ca2601c0 100644
--- a/lib/upgrade.txt
+++ b/lib/upgrade.txt
@@ -70,6 +70,8 @@ information provided here is intended especially for developers.
   is now a part of \antivirus_clamav\scanner class methods.
 * \repository::antivir_scan_file() has been deprecated, \core\antivirus\manager::scan_file() that
   applies antivirus plugins is replacing its functionality.
+* Added core_text::str_max_bytes() which safely truncates multi-byte strings to a 
+  maximum number of bytes.
 
 === 3.0 ===
 
diff --git a/search/engine/solr/classes/document.php b/search/engine/solr/classes/document.php
index c4ef6a89eb3..20c1f3ecf9a 100644
--- a/search/engine/solr/classes/document.php
+++ b/search/engine/solr/classes/document.php
@@ -53,7 +53,7 @@ class document extends \core_search\document {
     public static function format_string_for_engine($string) {
         // 2^15 default. We could convert this to a setting as is possible to
         // change the max in solr.
-        return substr($string, 0, 32766);
+        return \core_text::str_max_bytes($string, 32766);
     }
 
     /**