diff --git a/fillpdf.module b/fillpdf.module
index 34f19cf25569a57136d92131dcb7f43c4a4b9cf8..3137d542f38f0537500526bcb7ecb73a06124404 100644
--- a/fillpdf.module
+++ b/fillpdf.module
@@ -396,9 +396,9 @@ function fillpdf_merge_pdf($fid, $nids = NULL, $webform_arr = NULL, $sample = NU
         $fields[$obj->pdf_key] = $str;
       }
     }
-    
+
     // Apply prefix and suffix, if applicable
-    if ($fields[$obj->pdf_key]) {
+    if (isset($fields[$obj->pdf_key]) && $fields[$obj->pdf_key]) {
       if ($obj->prefix) {
         $fields[$obj->pdf_key] = $obj->prefix . $fields[$obj->pdf_key];
       }