diff --git a/web/includes/functions.php b/web/includes/functions.php
index 13b347893..537a9fa8e 100644
--- a/web/includes/functions.php
+++ b/web/includes/functions.php
@@ -2620,4 +2620,19 @@ function random_colour() {
     str_pad( dechex( mt_rand( 0, 255 ) ), 2, '0', STR_PAD_LEFT);
 }
 
+function zm_random_bytes($length = 32){
+  if ( !isset($length) || intval($length) <= 8 ) {
+    $length = 32;
+  }
+  if ( function_exists('random_bytes') ) {
+    return random_bytes($length);
+  }
+  if ( function_exists('mcrypt_create_iv') ) {
+    return mcrypt_create_iv($length, MCRYPT_DEV_URANDOM);
+  }
+  if ( function_exists('openssl_random_pseudo_bytes') ) {
+    return openssl_random_pseudo_bytes($length);
+  }
+  ZM\Error('No random_bytes function found.');
+}
 ?>
diff --git a/web/index.php b/web/index.php
index 2f1a6cf62..d5f261742 100644
--- a/web/index.php
+++ b/web/index.php
@@ -177,7 +177,7 @@ if ( isset($_REQUEST['view']) )
 
 
 # Add CSP Headers
-$cspNonce = bin2hex(openssl_random_pseudo_bytes(16));
+$cspNonce = bin2hex(zm_random_bytes(16));
 
 $request = null;
 if ( isset($_REQUEST['request']) )