diff --git a/lib/common.lib.php b/lib/common.lib.php
index 411554f16..2db6f7b28 100644
--- a/lib/common.lib.php
+++ b/lib/common.lib.php
@@ -2461,7 +2461,7 @@ function add_stylesheet($stylesheet, $order=0)
 {
     global $html_process;
 
-    if(trim($stylesheet))
+    if(trim($stylesheet) && method_exists($html_process, 'merge_stylesheet') )
         $html_process->merge_stylesheet($stylesheet, $order);
 }
 
@@ -2469,7 +2469,7 @@ function add_javascript($javascript, $order=0)
 {
     global $html_process;
 
-    if(trim($javascript))
+    if(trim($javascript) && method_exists($html_process, 'merge_javascript') )
         $html_process->merge_javascript($javascript, $order);
 }