diff --git a/lang/en/install.php b/lang/en/install.php
index 9d064809a6d..a0771134319 100644
--- a/lang/en/install.php
+++ b/lang/en/install.php
@@ -144,6 +144,7 @@ $string['inputdatadirectory'] = 'Data directory:';
 $string['inputwebadress'] = 'Web address :';
 $string['inputwebdirectory'] = 'Moodle directory:';
 $string['installation'] = 'Installation';
+$string['invaliddbprefix'] = 'Invalid prefix. The prefix can only consist of lower case letters and underscore.';
 $string['langdownloaderror'] = 'Unfortunately the language "{$a}" could not be downloaded. The installation process will continue in English.';
 $string['langdownloadok'] = 'The language "{$a}" was installed successfully. The installation process will continue in this language.';
 $string['memorylimit'] = 'Memory limit';
diff --git a/lib/installlib.php b/lib/installlib.php
index e8a4bc988ca..5144936a42c 100644
--- a/lib/installlib.php
+++ b/lib/installlib.php
@@ -179,6 +179,9 @@ function install_helpbutton($url, $title='') {
  * @return string
  */
 function install_db_validate($database, $dbhost, $dbuser, $dbpass, $dbname, $prefix, $dboptions) {
+    if (!preg_match('/^[a-z_]*$/', $prefix)) {
+        return get_string('invaliddbprefix', 'install');
+    }
     try {
         try {
             $database->connect($dbhost, $dbuser, $dbpass, $dbname, $prefix, $dboptions);