diff --git a/fillpdf.module b/fillpdf.module
index 5eaa5f55639f0d681ad3e225e44f1ac44935b108..6097c4b1d32540626701ad7cf51f73d54993952f 100644
--- a/fillpdf.module
+++ b/fillpdf.module
@@ -2074,7 +2074,7 @@ function fillpdf_pdftk_check($pdftk_path = 'pdftk') {
     return FALSE;
   }
   // Check if version output includes "pdftk".
-  elseif (!strpos($output, 'pdftk')) {
+  elseif (strpos($output, 'pdftk') === FALSE) {
     return FALSE;
   }
   return TRUE;